gi Ls 


Beas 


THEGETTY CENTERLIBRARY 


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PROSPECT STREET, RYE By T. K. GRANT, F.R.P.S. 


A photograph in natural colours, taken on the Autochrome plate, and reproduced by the 
four-colour process. 


=  CASSELL’S 
CYCLOPAEDIA OF 
PHOTOGRAPHY 


EDITED BY 
BERNARD E. JONES 


ILLUSTRATED BY TWENTY-FOUR FULL-PAGE 
PLATES IN COLOUR AND HALF-TONE, AND BY 
HUNDREDS OF LINE DRAWINGS IN THE TEXT 


VOLUME I 


CASSELL AND COMPANY, LTD. 
43-45 East 19th Street New York 
1912 | Ob 


LIST OF CHIEF 


T. THORNE BAKER, F.C3S. 
HENRY W. BENNETT, F.R.P.S. 


A. H. BLAKE, M.A. 
GEORGE E. Brown, F.I.C. 
THEODORE BROWN 


J. C. Burrow, F.R.P.S. 


CHARLES P. BUTLER, A.R.C.Sc. 
(Lond.), F.R.P.S., F.R.A.S. 


DRINKWATER BUTT, F.R.P.S. 
EDGAR CLIFTON, F.R.P.S. . 

F. MARTIN F.R.P.S. 
WILLIAM GAMBLE 

ARTHUR D. GODBOLD . 
WALTER KILBEY, F.R.P.S.. 
ARTHUR LOCKETT, Honours Silver 


Medallist in Photography, City and 
Guilds. 


DUNCAN, 


THOMAS MANLY, F.R.P.S. . 
J. I. Picc, F.R.M.S., F.R.PS. . 


Percy R. SALMON, F.R.P.S. 
Py, WALL, F.R.PSS. . 


W. L. F. WASTELL, F.R.P.S. . 


CONTRIBUTORS 


Isochromatic Photography, Photo- 
telegraphy 

Architectural Photography, Carbon 
Process, Lantern Slides, etc. 

Night Photography 

Copyright 

Stereoscopic Photography, Kine- 
matography 

Mine Photography 


Astronomical Photography 


Studio Design and Construction 
Lenses 

Natural History Photography 
Photo-mechanical Processes 
Studio Work 

Focal-plane Shutter Work 


Cameras, Apparatus, Special Pro- 
cesses, etc. 


Ozobrome, Ozotype 


Photomicrography, X-ray Photo- 
graphy 
Historic and General Processes, 


Developers and Miscellaneous 


Chemistry, Colour Photography, 
Special Processes 


Pictorial Photography and Special 
Processes 


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PREFACE 


ANY years ago, while assisting in the production of a small photographic 
manual, the difficulty experienced in finding room for everything that ought 
to have been included brought to my mind a suggestion for an encyclo- 

peedic work covering all the phases of photography. It was not until this suggestion 
had been discussed, seven years later, with Mr. Percy R. Salmon that it became crys- 
tallised into something concrete and workable. To Mr. Salmon, more than anyone 
else, is due the credit for the particular form which this work has assumed. ‘Together 
we planned it, and together decided the majority of the multitudinous questions of 
detail that arose. 

Of photographic dictionaries and cyclopedias printed in the English language 
there have been as many as could be counted on the fingers of one’s hands; but the 
present volume is essentially different from any of them, and is undoubtedly the most 
ambitious work of its kind yet projected. With possible exceptions, its predecessors 
were written or compiled from cover to cover by one hand; whereas this work is the 
result of the co-operation of many men, each having special knowledge of his own 
particular branch. Modern photography has so many ramifications, each calling for 
the application of special knowledge, that I felt that the only proper course, in attempt- 
ing to produce a photographic cyclopedia at once authoritative and complete, was 
to enlist the services of as many specialists as possible. About a score of the best- 
known and most authoritative expert photographic writers extended their co-operation, 
and their contributions constitute the bulk of this work. 

While it must be confessed that complete accuracy is almost too much to hope 
for in the first edition of a work of reference, I have taken care to do all that could 
be done to check and verify the statements made. My especial thanks in this connec- 
tion are due to Messrs. Percy R. Salmon, E. J. Wall, Arthur Lockett and William 
Gamble, for the trouble they have taken in reading the proofs. I shall appreciate 
and acknowledge any minor corrections that readers may send me, and shall hope 
to be able to incorporate them in later editions, in the happy event of such being 
called for. 

The scope of the work demands some words of explanation. The object has been 
to include every accepted photographic term and to survey the whole field of photo- 
graphic knowledge, whilst giving particular attention to the requirements of the 
working photographer, both amateur and professional. This cyclopzedia is intended 
essentially as a simple guide to photographic practice, whatever else it may be. In 
all cases where the process described is commonly used, or is likely to be worked 
nowadays, working directions and definite formule are given. 

This work is intended not only for the practical photographer, but also for the 
scientific student, who will find in all those articles that have been written especially 
for him valuable, because authoritative, summaries of what has already been attained 
in the many branches of photographic science. he manufacturer, too, especially the 
manufacturer of materials, will find in this volume a mass of information relating to 
what others have done before him, and by profiting by it he will be prevented from 
wasting time and money in useless trials in some directions and possibly be given 
ideas as to commercially remunerative lines of experiment in others. 


vi PREFACE 


There are two matters, in particular, upon which I think it desirable to address 
a word to the critical reader. It will be noticed that a few biographies are given, 
and the question as to why such and such men are included and others omitted is 
sure to arise. ‘The biography of no living photographer will be found in these pages } 
and with regard to the dead worthies, I have done my best to include only those 
who, when viewed historically, have real claims to distinction. And in such a matter 
much must be left to personal opinion. The other matter is the omission, with a 
few exceptions, of trade names. ‘Their inclusion, a highly debatable point, would 
have meant the addition of more than thirteen hundred headings, the informa- 
tion given under which might rapidly have gone out of date. The exceptions, as in 
the case of a certain camera which it would be superfluous to mention, have now 
become part of the language, and are associated in the public mind quite as much 
with broad types of apparatus or certain classes of materials as with any particular 
brands of manufacture. 

The illustrations call for a word of explanation. The monochrome plates have 
been selected as representing separate phases of photographic art, and are offered as 
being good examples of their kind. On the other hand, three of the coloured plates are 
intended to represent merely the capabilities of the screen plates with which the 
original pictures were made; while, of the remaining two, one plate shows the steps 
in the production of a four-colour print and the other the composition of six of the 
best-known screen plates. The line drawings throughout the book (almost all of 
which have been drawn by E. S. W. Cunnington from the contributors’ sketches) have 
the sole object of elucidating the text ; much thought was given to the advisability 
or otherwise of using photographic illustrations in the text, but it was decided that 
drawings would be far more instructive. In many cases the drawings have been 
based upon illustrations appearing in trade catalogues, and in this connection my 
thanks are due to a large number of firms, including the following: Adams & Co. ; 
A. H. Baird; Bausch and Lomb Optical Co.; R. and J. Beck, Ltd.; W. Butcher 
and Sons, Ltd.; J. J. Griffin and Sons, Itd.; J. Fallowfield; J. Halden and Co.; 
Houghtons, Ltd.; Infallible Exposure Meter Co.; Kodak, Ltd.; J. Lancaster and Son, 
Ltd.: Marion and Co., Ltd.; G. Mason and Son; Newman and Guardia, Ltd.; A. W, 
Penrose and Co., Itd.; Ross Ltd.; Sanger Shepherd and Co., Ltd.; O. Sichel and 
Co.; Thornton-Pickard Mfg. Co., Ltd.; W. Tyler; A. G. Voigtlander and Sohn ; 
Watkins Meter Co. ; W. Watson and Sons, Ltd.; Westminster Engineering Co., Ltd. ; 
Westminster Photographic Exchange, Ltd.; and C. Zimmermann and Co. 

For the principal information given in the article ‘‘ Ceramic Process ” I am indebted 
to Mr. W. Ethelbert Henry’s standard work, “‘ Photo-Ceramics.”’ 

With regard to the formule, in practically all cases the parts are given in both 
British and Metric measures ; by whichever system a solution is made up, the relative 
proportions of the ingredients will be almost exactly the same, although the actual 
quantities nearly always differ. 


B. EB J. 


LIST OF COLOURED PLATES 


a Prospect Street, Rye.” A Photograph on the Autochrome Plate. By 
T. K. GRANT, F.R.P.S. . ° . ° ‘ ° - Frontispiece 
, ; FACING PAGE 
Still Life «4 Photograph on the Dufay Dioptichrome Plate ° . ° ° , 07 
A Four-colour Print and the Consecutive Steps in its Production . 103 


Portrait. 4 Photograph on the Thames Plate By H. ESSENHIGH CORKE, 
F.R.P.S. . é 5 - : : - : fs : ; Sec yy 


Screen Plates for Photography in Natural Colours . : : - Ags 


LIST OF MONOCHROME PLATES 


FACING PAGE 


Studio Portraiture—‘ Portrait of A. Haddon.” By FurRLEY Lewis, 


F.R.P.S.. f ; . : ; ; . : : : ; 16 
Architectural Photography (Interior)—‘‘In Westminster Abbey.” By 

HENRY W. BENNETT, F.R.P.S. _ . ; . ; . : - 49 
Zoological ey Head of eed Ram.” By W. L. F, 

WASTELL, F.R.P.S. . ; ; m1 Oe 
Various Renderings of Daffodils in Blue Vase _. : ° : + S252 


Landscape Photography—‘*‘On Wisley Common.” By J. B. B. 
WELLINGTON, F.R.P.S. . : f : : ; : #146 


Night Photography. By A. H. BLAKE, M.A. ; ; : P SouOd 


Architectural Photography (Exterior)—‘‘Church of Notre Dame, 


Caudebec-en-Caux.” By H. W. BENNETT, F.R.P.S. . ° - 208 
Seascape and Skyscape Photography—‘“‘ After a Storm” 241 
Combination Printing—‘‘ Dawn and Sunset.” By (the late) H. P. 

ROBINSON . ; : ; , ‘ ‘ ; . 256 

289 


Home Portraiture. By PERCY R. SALMON, F.R.P.S. - ; ; 


viii LIST OF MONOCHROME PLATES 


FACING PAGE 


Kinematograph Films _. ; . : . . : ° : - 304 


Celestial PO Oy ee Moon.” Abgiaraohed at the Paris 
Observatory : ; : : eee 


Photomicrography — ‘‘Group of Insects’ Eggs.” By J. I. PiGG, 
F.R.M.S., F.R.P.S. : . : . . : ee 


Influence of the Lens on Perspective. By P. R. SALMON, F.R.P.S. 400 
Radiography, or X-ray ee ee —‘*A Head.” By J. I. PiGc, 


F.R.M.S., F.R.P.S. ; . . 448 
Firelight Effect. By H. ESSENHIGH CorKR, F.R.P.S. : : Mae fe 
Focal Plane Shutter Work. By WALTER KILBEY, F.R.P:S. . - 496 
Snow and Hoar Frost Photography. By (the late) Col. J. GALE . 529 


Telephotography—*‘ North Doorway, Rheims Cathedral.” By ERNEST 
MARRIAGE, F.R.P.S. ; : : ; ; - 544 


CASSELL’S 


Cyclopedia of Photography 


ABAT-JOUR (Fr.) (Ger., Schrige Fenster, 
Oberiicht) 

A skylight or aperture for admitting light to a 
studio, or an arrangement for securing the same 
end by reflection. In the days when studios for 
portraiture were generally found at the tops of 
buildings not originally erected for that purpose, 
and perhaps in narrow thoroughfares or with a 
high obstruction adjacent, it became necessary 
to obtain all the available top light. This alone, 
however, is not well suited for artistic lighting, 
a side light being usually preferable. The abat- 
jour, therefore, was so designed as to give what 
was ptactically a side light, although coming 
ptincipally from above. A style much used 
formerly, and still occasionally met with, is 


Two Styles of Abat-jour 


shown at A. Into a bevelled opening cut in the 
wall, the roof, or both, is let a slanting glazed 
frame. Another form (B) is an inclined box- 
like structure open at the top and furnished with 
a mirror, or painted white inside, to reflect light 
downward through the window or glazing. The 
teflector used in daylight enlarging is really an 
application of the latter kind of abat-jour, by 
which the light, falling vertically from the sky, 
is reflected in a horizontal direction on the nega- 
tive in the enlarging camera. 


ABAXIAL 
Away from the axis. A term applied to the 
oblique or marginal rays passing through a lens. 


ABBE CONDENSER 
One of the most popular types of substage 
condensers for the microscope and used in photo- 
1 


micrographic work. It is made in two forms. 
The first consists of two lenses, and is of low 
numerical aperture. The second, used for high- 
power objectives, has three lenses, and is of 
higher numerical aperture (N.A.). 


ABBE, ERNST 

Professor Abbe died at Jena on January 14, 
1905, aged 65 years. He was associated with the 
optical firm of Carl Zeiss, and paid particular 
attention to microscope objectives, with which 
his name is now generally connected. In 1881 
he took an interest in the smelting of new optical 
glasses which was being made by Dr. Schott, 
and this was the beginning of the Jena glass 
factory of Schott and Genossen, the products of 
which have been used by lens makers as the raw 
materials of the large-apertured lenses known as 
anastigmats. Professor Abbe was the first to 
apply these glasses in a practical way to photo- 
gtaphic lenses. On the death of Carl Zeiss in 
1888 Professor Abbe became sole proprietor, 
and in 1896 he introduced an arrangement by 
which the employees became practically the 
owners of the business. 


ABERRATION (Fr., Aberration; Ger., Abir- 
vung) 

A term used in photographic optics to express 
afaultinalens. (See ‘“‘ Chromatic Aberration,” 
‘Spherical Aberration,” ‘“‘Curvilinear Distor- 
tion,” ‘‘ Astigmatism,” etc.) 


ABRADING POWDER 

Rubbed on the smooth surface of dried nega- 
tives and bromide enlargements in order to give 
a “‘ tooth ’’ for subsequent pencilling. Such abra- 
sives as pumice, cuttle-fish bone, etc., are gener- 
ally used, and these must be very finely ground 
and be free from grit. On negatives the powder 
is rubbed on lightly with the finger-tip, but on 
bromide prints it is applied with a leather stump. 
An excellent abrading powder for negatives con- 
sists of 1 part of powdered resin and 2 parts of 
cuttle-fish bone, the whole being sifted through 
silk. Cigar or tobacco ash also serves the pur- 
pose. Negatives may be reduced by means of a 
moist abrading mixture as described under the 
heading ‘‘ Baskett’s Reducer.’’ Various grades 
of emery powder and carborundum are used 
in lens and sereen grinding, etc. 


Abrasion Marks 


In process work, pumice and emery powders are 
used with water for cleaning or polishing zinc 
or copper. Fine emery powder is employed for 
graining the thick glass plates used for collotype 
printing. Pumice powder is used for removing 
gloss from prints that have to be retouched. 


ABRASION MARKS 

Black or pencil-like markings upon bromide 
and gaslight papers, chiefly occurring on glossy 
surfaces. They are seen only upon the finished 
print, and are due to pressure upon the gelatine 
film, and particularly to scratching against the 
printing frame or edges or corners of the packet 
when withdrawing the sheets. Handling the 
paper carefully will prevent them, and the use 
of a special developer, such as the following, 
will generally be of assistance :— 


Metol 34 gts. 3-4 g. 
Hydroquinone . Rye 68 eee a 
Sodium sulphite . He ta ypaet Baty 
Sodium carbonate CaO Aa0>; 
Potass. iodide . ba ld oye 
Potass. bromide (10 %) 36 drops 4 drops. 
Water to 20 OZ. 1,000 ccs. 


Any other metol-hydroquinone developer may 
be used if 1 grain of potassium iodide is added 
to each ounce of developer used. The addition 
of potassium cyanide is also resorted to, the 
proportion being 3 or 4 drops of a 10 per cent. 
solution to 1 oz. of developer. But the use 
of a special developer does not answer for all 
papers. Abrasion marks may often be removed 
from the finished print by rubbing lightly with 
a pad of cotton wool soaked in water, weak 
ammonia (5 drops per ounce of water), or methyl- 
ated spirit. An _ effective—although rather 
troublesome—plan is to immerse the finished 
print for one minute in the following solution :— 


Potass. iodide . 20 gts. 2 g. 
Iodine : s Spe MENS O'2 ,, 
Water . 20 02. 1,000 ccs, 


When the white parts of the print turn blue, 
transfer to a fresh “‘hypo”’ fixing bath for five 
minutes, and then wash thoroughly. If the 
iodide bath is allowed to act too long, it acts 
as a reducer. 


ABSORPTION (Fr., Absorption; Ger., Absorp- 
tion) 

This term is used both in a chemical and an 
optical sense. In the former sense it is used to 
designate the taking up of one substance by 
another, just as a sponge absorbs or sucks up 
water. As a rule, this is not accompanied by 
any chemical, but merely a physical change. 

Optically, absorption is applied to the sup- 
pression of light, and to it are due all colour 
effects (see ‘‘ Colour’). It is of great import- 
ance from a photographic point of view, as on 
Draper’s law, according to which only those 
rays which are absorbed by a substance act 
chemically on it, is based the whole of the photo- 
chemical action of light. Light, when absorbed, 
is not lost but is converted into some other form 
of energy, either heat or chemical action. The 
absorption spectra of dyes are of great interest, 
as by their aid it is possible to prepare colour 
filters of any given tint. Many substances and 


Absorption 


dyes have simple absorption spectra—that is to 
say, more or less well defined continuous por- 
tions of the spectrum are absorbed; other sub- 
stances, on the other hand, such as chlorophyll, 
have complicated absorption spectra, which 
change in character according to the concen- 
tration of the solution, or the depth of the solu 
tion, which is practically the same thing. 

The position and shape of the absorption bands 
of a substance are in many cases so characteristic 
that they serve as a means of identification. 
Obviously, the most opaque substances are the 
metals, but even these are translucent in thin 
films; silver, for instance, appears blue, whilst 
gold in thin films is green. Even such trans- 
parent and colourless substances as water, 
alcohol, glycerine, etc., possess characteristic 
absorption spectra, and therefore appear coloured 
when in sufficiently thick films. In studying the 
absorption spectra of coloured solutions, either 
the visual or the photographic method may be 
used, and the latter will be found not only more 
reliable, but considerably quicker. The visual 
method can obviously be applied only to the 
visible portion of the spectrum, whilst by the 
aid of photography the ultra-violet and infra- 
red regions can also be mapped out. 

Dr. Kenneth Mees and S. H. Wratten, who 
have made a special study of dye absorption 
spectra by photographic means, give the following 
outline of the methods which may be adopted : 
‘“*(1) One may take a series of photographs with 
increasing dilution of the dye; (2) one may 
take a series of photographs with a constant 
concentration of the dye, but an increasing 
thickness of the cell; (3) one may take a 
series of photographs with a constant con- 
centration and constant cell thickness, but 
with a varying exposure. These three methods 
will all produce results differing slightly, though 
(1) and (z) are nearly equivalent to one another. 
(1) is a very slow method, and it would be 
probably quicker to use a spectro-photometer. 
(2) and (3), though quicker, are still slow if 
carried out as described. But if in method (2) 
instead of varying thicknesses of cell there is 
used a cell of which the thickness varies through- 
out the length—that is to say, a wedge-shaped 
cell placed in front of the slit so that the thick- 
ness of the layer of dye solution in front of the 
slit varies from end to end of the slit—the method 
resolves itself into taking one or possibly two 
photographs of each dye. Method (3) is inferior 
to the two other methods, as it involves the inter- 
pretation of the photograph of the plate curve. 
It is, however, a convenient way of examining 
the absorptions of coloured films and filters,” 
This method is most conveniently carried out by 
placing directly in front of the slit a small wedge 
of black glass so that the intensity of the light 
varies from end to end of the slit. This black 
wedge consists of a narrow prism of neutral tinted 
glass cemented to a similar prism of white glass, 
which of course destroys the prismatic effect by 
forming a parallel plate. With this the intensity 
of the light varies from 1 to 10,000. 

For visual measurement of absorption spectra 
a spectro-photometer is used. This consists of 
a spectroscope and some means of comparing 
the brightness of two spectra of one light source. 
This can be effected in several ways, as, for 


Accelerator 


instance, by two slits, which can be independently 
opened or closed, or by polarising prisms. The 
disadvantage of the variable slit system is that 
the two spectra are of unequal purity, and 
therefore accurate readings are impossible. In 
the polarising spectro-photometers the slit is 
usually divided across the middle by a small bar 
of metal, and the two light beams are polarised 
and dispersed, or dispersed and polarised, equality 
being obtained by rotation of a Nicol prism. The 
two spectra are brought into juxtaposition at the 
eyepiece, and equality of illumination obtained 
throughout its length. As one spectrum is con- 
tinuous and the other darkened Ly the absorption 
band, the former is reduced in brightness till the 
two are equal and the necessary readings obtained 
from the varied width of the slit or the angle 
through which the Nicols are turned. The 
transmitted light, divided by the incident light, 
which is always taken as unity, equals the 
extinction coefficient. 


ACCELERATOR  (Fr., 
Beschleuniger) 


A substance added to developing solutions to 
shorten the duration of development and bring 
out the image more quickly. Usually it is an 
alkali which hastens the development owing to 
its power of absorbing the bromine set free from 
the silver salt during development, thus forming 
an alkaline bromide which acts as a restrainer, 
and as this increases with continued or repeated 
use of a developer, due allowance should be made. 

Common accelerators are sodium carbonate, 
washing soda, ammonia, potassium carbonate, 
sodium hydrate (caustic soda), and potassium 
hydrate (caustic potash). “‘ Hypo’’ (sodium hypo- 
sulphite) has been recommended when develop- 
ing with a mixture of ferrous-oxalate, but not 
infrequently it causes a partial reversal of the 
image; merely adding a few drops of a weak 
solution of “‘hypo” to the normal developer has a 
wonderful accelerating effect in some cases. 
Attempts have been made to introduce substi- 
tutes for alkaline accelerators in the form of 
acetone with sodium sulphite, tribasic sodium 
phosphate, and other chemicals, but only the 
two named have met with any success. Some 
*“one solution’? developers—such as rodinal, 
azol, etc.—include an accelerator; but in “ two 
solution ’’ developers, the developer proper is 
generally included in bottle “A” or “No. 1,” 
and the accelerator in-bottle “‘B” or ‘‘ No. 2.” 
It was long thought that an increase of the 
accelerator in cases of under-exposure brought 
out more detail, but photographers are now 
growing out of the idea. It is never advisable 
to add much alkali, because this invariably tends 
to produce fog. Accelerators cannot be used 
as the fancy dictates, some being more suitable 
for certain developers than others. Ammonia 
and sodium carbonate, for example, are found 
to give their best results in conjunction with pyro. 
Some of the newer developers—amidol, for 
example—do not require an alkali accelerator, 
and they will work with sodium sulphite, which 
is a preservative rather than an accelerator. In 
regard to the comparative strengths of the 
numerous alkalis used for accelerating develop- 
ment, a table will be found under the heading 
** Alkalis, Chemical Equivalence of.” 


Accélévateur ; 


Ger., 


Acetic Acid 


ACCOMMODATION OF THE EYE (See 
** Axial Accommodation.’’) 

ACCUMULATOR (Fr. Accumulateur; Ger., 
Akkumulator) 


Accumulators or storage batteries are used in 
X-ray work when the electric current cannot be 
obtained from mains. An accumulator consists 
of a series of lead grids filled in with lead oxide 
and immersed in dilute sulphuric acid. The 
potential of an accumulator when fully charged 
is 2 volts, and recharging is necessary when it 
falls to 1°8. Current is always leaking from 
accumulators even when not in use, and they 
should therefore be recharged at least once a 
month, or the plates will be ruined. The posi- 
tive terminal of a cell is painted red, the nega- 
tive black. In coupling up two or more cells the 
positive terminals are connected up with the 
negative terminals, the free terminals being then 
connected with the induction coil. A coil giving 
a 10-in. spark requires from six to eight accumu- 
lators, supplying a current of 5 to 10 ampetes. 


ACETALDEHYDE 


ACETATES 

Salts formed by acting upon metals or their 
oxides with acetic acid. Examples are lead 
acetate, sodium acetate, etc., etc., which are 
described under their own headings. 


ACETIC ACID (Fr., 
Essigsadure) 

Also known as purified pyroligneous acid. 
HC,H;0,. Molecular weight, 60. There are 
three kinds of acetic acid :—(1) glacial, con- 
taining about 99 per cent. of acid and 1 per cent. 
of water (sp.g., 1:°065); glacial acetic acid is the 
most widely used for photographic purposes, and 
receives its name from the fact that it solidifies 
and freezes into long ice-like crystals at com- 
paratively low temperatures; (2) commercial 
‘** strong,’’ about one-third the strength of the 
glacial variety, and containing about 33 per 
cent. of acid, sometimes known as Beaufoy’s 
acetic acid (sp.g., 17044); (3) dilute acetic acid, 
made by mixing 1 part of the “strong” acid 
with 7 parts of water (44 per cent.), and sold as 
‘* distilled white vinegar ’’ (sp.g., 17006). Acetic 
is the oldest of acids, and is given in old diction- 
aries as “‘ acetous acid.’”’ Its impurities may be 
hydrochloric, sulphuric and sulphurous acids, 
but most samples sold by chemists are quite 
pure enough for photographic purposes. Acetic 
acid readily dissolves in water, alcohol, and 
ether; it is a strong escharotic, causing painful 
blisters if allowed to remain on the skin, but 
the application of a solution of soda or any other 
alkali will at once neutralise it. It is extremely 
volatile, and should be kept in a glass-stoppered 
bottle and in a cool place. It has many uses in 
photography, and in the early days, when it 
cost as much as 8d. per ounce, was largely used 
as a constituent of the developer for wet plates. 
Nowadays, it is used for clearing the iron out of 
bromide prints after development with ferrous 
oxalate, to assist uranium toning, and, on rare 
occasions, as a restrainer when developing with 
hydroquinone. Acetic acid is a solvent for 
cellwoid, gelatine, and pyroxyline. 


(See ‘* Aldehyde.’’) 


Acide acetique; Ger., 


Acetic Ether 


€ 


In process work, acetic acid is used in the iron 
developer for wet plates. The amount required 
increases as the working temperature increases ; 
at 60° F. 4 oz. of glacial acetic acid to 20 oz. of 
developer is a suitable proportion. The acid 
retards the action of the ferrous sulphate. A 
mixture of acetic acid and salt is used for clean- 
ing up the copper plates during half-tone etching 
to enable the etcher to see the image better when 
proceeding to re-etch. It is also used for remov- 
ing the magnesia that is rubbed into the etched 
plate to make the image visible. 


ACETIC ETHER (Fr., Ether acétique, Acétate 
ad éthyle ; Ger., Essigaether) 

Synonym, ethyl acetate. CH 3 CO O(CeH;). 
Molecular weight, 89. Solubilities, 1 in 17 water, 
miscible in all proportions with alcohol and 
ether. It should be kept in well-stoppered 
bottles away from fire, as the vapour is very 
inflammable. A light, volatile, colourless liquid, 
with pleasant acetous smell, obtained by dis- 
tillation from alcohol, acetic acid, or sodium 
acetate with strong sulphuric acid. Sometimes 
used in making collodion. 


ACETOL (Fr., Acétol; Ger., Acetol) 

A gelatine with an acetic acid substratum, 
used for collodion emulsion, It is said by its 
advocates to give a beautiful surface and spotless 
negatives. 


ACETOMETER (Fr., Acétométre ; Ger., Aceto- 
meter ) 
A hydrometer specially graduated to show 
the sttength of acetic acid. 


ACETONE (Fr., Acétone; Ger., Aceton) 

A colourless volatile liquid of peculiar and 
characteristic odour, having the formula C3; H, O 
or CH; CO CH;. It is met with commercially in 
various qualities. It is miscible in all propor- 
tions with water, alcohol, and ether. As the 
vapour is highly inflammable, the liquid should 
be kept in a bottle with a close-fitting cork or 
glass stopper. Acetone has two separate and 
distinct uses in photography, as an addition to 
developers and in varnish making. It acts as 
a solvent for resins, camphor, celluloid, etc., and 
should therefore never be used for films or in 
a celluloid dish. 

As a constituent of a developer acetone works 
best perhaps with pyro in the following one- 
solution form :— 


Pyro : 4 ; . 180 gts, 18g 
Sodium sulphite (crystals) 1,120 ,, bb i 
Acetone . : : 24 mins. 2°4 ccs, 
Water to 20 0z. 1,000 ,, 


It may, however, be used with other developers. 
When mixed with sulphite it forms acetone 
sulphite, and the soda of the sulphite combines 
with the developing agent to form a pheno- 
late, so that it may be used in place of an 
alkali when sulphite is present. It gives a very 
clean-working developer, moderately free from 
stain, and hardens the gelatine, or at any rate 
does not soften it as alkalies do. As a developer 
for paper prints it is best when combined with 
metol-hydroquinone in the following form :— 


Acetylene Generator 


Metol a : 27 gts. 2°72. 
Sodium sulphite 54 0z. 20 E 
Hydroquinone . 88 gts, aS 
Potass. bromide (10 %) 22 mins. 22s 
Acetone. ‘ . 40 drms, 25 ccs 
Water to . 2002, 1,000 ,, 


This is a one-solution developer which, as above 
compounded, is ready for use for both plates 
and papers. 


ACETONE SULPHITE (Fr., Acétone sulfite; 
Ger., Acetonsulphit) 

A compound of acetone with acid sodium sul- 
phite, introduced as a substitute for sodium sul- 
phite and the metabisulphites for development. 
It has the form of a white powder, and its formula 
is NaHSO, CO(CH3), H,O. It is soluble in 
water (up to 50 per cent.), but less so in alcohol, 
and it is used for making concentrated forms of 
developers, also for fixing baths and to blacken 
negatives after being bleached with mercury. 
Unlike acetone itself, it does not make the 
developer active, and consequently an alkali or 
a carbonate must be used. Ten parts of acetone 
sulphite are equivalent to 7 parts of potassium 
metabisulphite or 20 parts of anhydrous sul- 
phite of soda (40 of soda sulphite crystals) in 
a developer. As a preservative for pyro, 4 oz. 
of acetone sulphite should be added for each 
ounce of dry pyro used. 


ACETOUS ACID 
The old, and now obsolete, name for acetic 
acid (which see). 


ACETYLENE (Fr., Acétyléne; Ger., Acetylen) 

A hydrocarbon gas (C,H,) having, when pure, 
a sweet odour, the well known unpleasant smell 
associated with this gas being due to the pre- 
sence of impurities. It burns in air with a very 
bright flame, and is largely used by photographers 
for studio lighting, copying, etc., and as an 
illuminant in enlarging and projection lanterns. 
It is produced by the action of water upon 
calcium carbide (which see), 1 lb. of which will 
yield about 5 ft. of gas. It was first described 
and demonstrated in the year 1836 at a meeting 
of the Royal Dublin Society under the auspices. 
of Edmund Davy, a professor of chemistry, and 
was brought into commercial use about half a 
century later by the discovery of the modern 
method of manufacturing calcium carbide in the 
electric furnace. Acetylene forms, like other 
combustible gases, an explosive mixture with 
ordinary air, the presence of as little as 4 per 
cent. of the gas being sufficient to constitute a 
dangerous combination. It was in the early 
part of 1895 that photographers began to turn 
their attention to the photographic value of 
acetylene, and photometric tests prove that 
acetylene has eight times the actinic power of 
the average incandescent gas mantle. As an 
illuminant in optical lanterns, acetylene is better 
than the incandescent gas mantle, but not so 
good as limelight. (See “ Optical Lantern Illu- 
minants.’’) 


ACETYLENE GENERATOR (Fr., Générateur 
d’acétyléne; Ger., Acetylengasentwickler) 


An apparatus for generating acetylene by the 
action of water on calcium carbide. Of the two 


Acetylene Generator 


types of generators, that is probably the better 
in which the carbide is immersed in or dropped 
into the water, as when water is permitted to 
fall on the carbide great heat is created, tending 
to the production of inferior gas, and the evolu- 
tion of oily products which are liable to accu- 
mulate in the pipes. However, many generators 
in which the water drips very slowly on the 


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Vey 
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A. Bucket-type 
Acetylene Generator 


B. Hopper and Valve- 
type Acetylene Generator 


carbide, as in the majority of acetylene lamps 
for cycle use, have a high reputation. Carbide 
to water generators are illustrated herewith. In 
the apparatus shown at A the water is contained 
in the tank E, in which slides the gas bell or 
reservoir F. The receptacle G, filled with lump 
carbide, is suspended from the top of the reservoir, 
which falls by its own weight, acetylene beginning 
to generate directly the carbide comes in contact 
with the water. The gas, filling the reservoir, 
causes it to rise and lifts the carbide receptacle, 
thus stopping further generation until by the 
consumption of the gas the reservoir again falls. 
The carbide receptacle is introduced or removed 
by extracting the tightly-fitting plug H. In the 
generator shown at B granulated carbide is 
contained in the hopper G, in which is a small 
opening or valve closed by the conical plug J. 
The plug is attached to a rod having a weight K 
asitslowerend. ‘The reservoir falls when empty, 
until the weight strikes the bottom of the water 
tank, this causing the rod to push up the plug 
J, allowing a small quantity of carbide to fall 
through the opening. The ascent of the reservoir 
as gas is generated raises the weight, which pulls 
down the plug and again closes the aperture. 
B is better in principle than A, as the carbide is 
acted upon in smaller quantities at a time. 

In all the earlier generators the carbide re- 
ceptacle was attached to the reservoir, causing 
an unnecessary pressure, and one also that varied 
as the carbide was consumed. Another dis- 
advantage was the fact that the waterseal was 
furnished from the same water as that used for 
generation. In the devices shown at C and D 
these objections are obviated. In the former of 
these the plug J is weighted to keep it normally 


Acetylene Generator 


closed, and its rod is connected at its upper end 
to a T-piece, this being in turn pivoted at each 
side to angle irons, which carry wheels at their 
outer ends. The reservoir F, in falling, depresses 
the angle irons, and these raise the plug rod by 
means of the T-piece, thus liberating a small 
charge of carbide. The plug is re-closed by the 
weight as the gas-laden reservoir rises. In 
the device shown at D the hopper ¢c containing 
the carbide has an upward-closing plug j fixed 
to a rod. The reservoir F in falling presses on 
the top of the rod and opens the plug, while the 
spring I, serves to return the rod and close the 
opening when the reservoir rises. 

Except when the carbide is dropped in small 
quantities into a sufficient excess of water, a 
washing apparatus of some kind is called for. 
If any quantity of acetylene is made, it is better 
also to remove the remaining impurities by 
passing the gas through calcium chloride with 
which is mixed a little unslaked lime, the mixture 
being contained in muslin bags arranged on 
perforated shelves, one over the other, in the 
purifier. A similar mixture is sold ready-pre- 
pared, and with this no bags or shelves are 
required, the lumps being merely packed in the 
receptacle. 

The pressure should not rise above two or 
three inches of water in the generator, and the 
pipes should not be less than % in. diameter. 
All taps must be well ground in, and should be 
lubricated with vaseline to prevent the corrosive 
action exerted by acetylene on  brasswork. 
Since the gas leaks more easily than ordinary 
house gas, greater care must be taken with all 
joints. Tar and paint are quickly affected, 


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D. “ Dreadnought ” 
Acetylene Generator 


C. “Ever Ready” 
Acetylene Generator 
and should not be used for this purpose; red- 
lead or white-lead, applied sparingly, is best. 
To detect a leak, a solution of soap and water 
may be applied, noticing if bubbles appear. 
In starting, the first gas coming off should be 
allowed to escape, as it contains an admixture 
of air. ‘The generator should be kept at least 
8 ft. or 10 ft. distant from any light, and no 
light should be at hand when emptying it after 
use. Copper should not be employed in acetylene 


Acetylide Emulsion 


generators, as under certain conditions a deton- 
ating explosive compound is formed. The best 
material for the body is tinned or galvanised 
sheet-iron, brass being used only for taps. 
Special burners are required for acetylene. 
The best are of steatite, on the air-injector 
principle. For photographic use, Bray’s 00000 
(acetylene) burners are perhaps most suitable. 
Fifteen of these, mounted in a white reflector, 
can be employed for studio portraiture, but a 
slightly larger number is better. Two-, three-, 
and four-burner jets are made for optical lantern 
and enlarging purposes. The soot that soon 
collects on the burners may be removed with a 
toothbrush or anything similar, while the holes 
may be cleared with a fine needle or wire. 


ACETYLIDE EMULSION 

Wratten and Mees prepared a silver acetylide 
emulsion by passing acetylene into ammoniacal 
solution of silver nitrate and emulsifying the 
precipitate, which is very explosive, in gelatine. 
They found that it blackened in daylight about 
ten times faster than silver chloride paper, but 
could obtain no evidence of the formation of a 
latent image with short exposures. 


ACHROMATIC (Fr, 
A chromatisch) 

A photographic lens is said to be achromatic 
when the visual image as focused upon the 
ground glass falls upon the same plane as the 
actinic image which forms the impression upon 
the sensitive surface. In telescopes and micro- 
scopes, achromatism means that the visual 
images are free from colour fringes, but it is 
quite possible for a photographic lens to show 
these fringes upon the focusing screen and yet 
to be capable of giving a sharply defined image 
upon the plate. ‘‘ Actinic” is a better term to 
use in connection with photographic instruments 
than achromatic. (Sce also ‘“* Chromatic Aberra- 
tion.’’) 


ACHROMATISM 
The condition of being achromatic. 


ACID BLAST 

The name given to an etching machine for 
process work, invented by Louis E. Levy, of 
Philadelphia. The working principle is that the 
acid is blown up to the plate, by means of air 
under compression, from a series of atomisers 
or sprays projecting upwards; a partial vacuum 
is maintained in the etching chamber above 
them, and the plate is held face downwards, and 
slowly moved to and fro horizontally to equalise 
the etching. 


ACID CHROMATE OF POTASH 
** Potassium Chromate.’’) 


ACID DEVELOPERS 
A term usually applied to ferrous sulphate and 
other wet-plate developers in an acid condition. 


ACID FIXING BATH 

The “hypo” (hyposulphite of soda) fixing 
bath made acid. Ordinary ‘‘hypo”’ fixing baths 
are neutral, not acid; but acid fixing baths 
may be used for negatives and bromide and gas- 


Achromabique; Ger., 


(See 


Acid Resist Varnish 


light prints, although not for prints on print- 
out papers. Their advantages are that they 
immediately stop the action of the developer, 
prevent stains, and keep quite clear in use. It 
does not do simply to add any acid—say sul- 
phuric or hydrochloric—to an ordinary “hypo”’ 
bath, inasmuch as this causes a yellow pre- 
cipitation with the accompanying evolution of 
sulphuretted hydrogen, which militates against 
the permanency of the prints. Sulphurous acid, 
however, may be added to an ordinary hypo 
fixing bath in the proportion of 2 drms. to 
I pint. The best acid fixer is made by adding a 
little potassium metabisulphite to the ordinary 
solution of “‘hypo”’; the exact proportions are of 
no importance, $ oz. to 1 pint being, however, 
a good average. The following is a precise 
formula suitable for prints :— 


Sodium hyposulphite . 3 02. 
Potass. metabisulphite. $5, ry a 
Water * . 2055 1,000 cCs. 


This is suitable for negatives if the “hypo” is 
increased to 40z, A cheaper form of acid fixer 
is the following :— 


150 g. 


“Hypo” solution (1 in 5) 25 oz. 1,000 ccs. 
To which add a mixture of :— 
Tartaric acid solution 
(1 in 2). : 2 OZ. 30 ccs. 


Sodium sulphite solu- 
tion (I in 4) . iz ” 79 5 
There is a danger of overworking acid baths 
and consequently of not fixing properly, as the 
clearness of the solution is apt to lead to the 
belief that it is still in a good working condition, 
although really it may be partly exhausted. 


ACID OXALATE OF POTASH 
“* Potassium Oxalate.”’) 


ACID RESIST 

A term applied in process work to all sub- 
stances used to form the image or protecting 
coating which prevents portions of the metal 
from being attacked. Practically all resinous 
bodies—bitumen, pitch, waxes, lacs, indiarubber, 
guttapercha—and fatty bodies form acid resists. 
Talc, graphite, silica, sulphur, carbon, and other 
inert bodies also form acid resists when dusted 
on to an image of atacky nature. Non-corrosive 
metals form another class of resists, as the 
image may be formed by a metal that is not 
attacked by the acid, which, however, attacks 
the base plate. Colloid bodies—such as gelatine, 
glue, gums, and albumen—also form acid resists, 
as in the so-called ‘‘ enamel process ” (which see). 
Acid resists are applied as varnishes for protect- 
ing the back and margins of the plate, as etching 
grounds, for scratching or engraving through with 
needle points and gravers, as etching inks, paints, 
dusting powders, light-sensitive films, electro- 
lytic deposits, fused metals. They are used for 
relief and intaglio etching, for lithography on 
stone, zinc, and aluminium, for protecting vessels 
and other articles used for etching, and for elec- 
trolytic etching or deposition. 


ACID RESIST VARNISH 
Shellac is probably the best and most used 
of the gum resins as a resist varnish. Cover 


(See 


Acid Stain Removers 


the shellac with wood alcohol, and leave for a 
few hours to dissolve. For 4 oz. of shellac about 
8 oz. of methylated spirit will be required, and, 
for colouring, about 2 drms. of methyl violet 
dye. To prevent the varnish setting too hard, 
add to every pint about 4 oz. of linseed oil. 

Shellac varnish is said to contain impurities 
which, when exposed to light, become insoluble, 
so that the varnish is difficult to remove; the 
remedy is to add 60 drops of oil of lavender to 
each pint of varnish, and use the varnish a little 
thinner. 


ACID STAIN REMOVERS 

Acid solutions used for clearing away stains 
caused by developers. Their use is open to 
objection, as fully explained under the heading 
“Stain Removers.” 


ACID SULPHITE (See ‘‘ Sodium Bisulphite.’’) 


ACIDS (Fr., Acides ; Ger., Sduren) 

Hydrogen compounds, which have a sharp 
taste and redden blue litmus paper. Acids may 
be solid, liquid, or gaseous, and are divided into 
strong and weak, organic and inorganic. Organic 
acids are usually such as contain carbon, whilst 
inorganic are those containing a metal. A 
further subdivision is made as to hydrogen or 
oxy-hydrogen acids ; of the former, hydrochloric 
acid HCl is an example, and of the latter, sul- 
phutic acid H,SO‘, as this contains oxygen as 
well as hydrogen. Acids are further differen- 
tiated into mono-, di-, tri-, etc., basic acids, and 
this refers to the number of molecules of hydrogen 
which are replaceable by a metal. For instance, 
nitric acid HNO; is monobasic, and forms salts 
of the typical formula XNO, (X here being a 
metal), Dibasie acids can be exemplified by 
oxalic acid, H,C,0,, which would form a salt 
having the composition of X,C,0,—e.g. KeC,0,, 
oxalate of potash. An example of a tribasic acid 
is boric acid H3;BO;, which forms borates X;BOs. 

In process work, acids play an important part. 
‘Nitric acid is almost exclusively the mordant 
used for etching zinc. Acetic, chromic, citric, 
fluoric, formic, gallic, hydrochloric, nitrous, 
phosphoric, picric, and tannic acids are all used 
in photo-mechanical processes. 


ACIDS, TESTS FOR 

Whilst strictly belonging to the domain of 
chemistry, it may be useful to give the usual 
tests for the acidity or otherwise of a solution. 
Blue litmus paper is reddened by acids. Phenol- 
phthalein solution (30 grs. in 10 oz. alcohol), a 
colourless solution, is reddened by alkalis, and 
the colour discharged by acids. Methyl orange 
(4 gts. in 10 oz, of water), an orange solution, 
turns pink with acids. 


ACLASTIC (Fr., 
tisch) 
Not capable of refracting, or bending, light. 


ACRIDINE YELLOW AND ACRIDINE 
ORANGE NO (Fr., jaune d’acridine, 
Orangé d’acridine NO; Ger., Akridingelb, 
Akridinorange NO) 

Two complex basic aniline dyes which have 
been suggested as sensitisers for emulsion work. 


Aclasiique; Ger., Aclas- 


Actinic 


They ate two of the most powerful sensitisers 
for green, but have found no practical application, 
as they stain gelatine very deeply, alcohol alone 
removing the stain. 


ACROGRAPH (Fr., Acrographe; Ger., Akro- 
graph) 

An engraving machine invented by N. S. 
Amstutz, an American engineer. Its essential 
features are a revolving cylinder and an engrav- 
ing tool—a V-shaped graver—carried along 
parallel to its axis; a phonograph, or a screw- 
cutting lathe, gives the idea. A photographic 
gelatine relief, such as a carbon transfer on cellu- 
loid with the image in perceptible relief, is 
wrapped round the cylinder, and over this relief 
is stretched a sheet of thin celluloid. As the 
cylinder revolves, a spiral thread is cut on the 
celluloid, this having the effect of making cuts 
in straight lines across the picture, but as the 
tool passes over the relief it cuts more or less 
deeply, according to the light and shade of the 
picture. Thus it reproduces the photograph as 
a kind of half-tone. The celluloid cutting can be 
printed from direct, or it can be made to serve 
as a matrix for electrotyping and stereotyping. 
By filling in the lines with transfer ink it can 
be used as a lithographic transfer, or by filling 
them with any opaque substance it can be used. 
as a negative for printing an image on to metal. 
The elaborations from the simple principle 
outlined above are in the form of micrometer 
adjustments for the tool, a microscope and 
electric lamp for watching the progress of the 
cutting and for setting the tool, and dividing 
wheels for varying the pitch of the lines. 


ACROMETER (Fr., Oléométre ; Ger., Oelwage) 
A kind of hydrometer specially graduated 
for testing the specific gravity of oils; known 
also as an oleometer or oil tester. An instru- 
ment of this description is sometimes useful for 
verifying the purity of the oils used in certain 
photographic and photo-mechanical processes. 


ACTINIC (Fr., Actinique; Ger., Aktinisch) 

A term applied to light that is rich in actinism, 
this being the property of light that causes 
chemicals to combine and decompose. In the 
early days of photography it was assumed that 
only the ultra-violet, violet, and blue rays were 
chemically active or actinic, hence these regions 
of the spectrum were so termed. Later researches 
have proved that it is practically merely a ques- 
tion of length of exposure which determines the 
photo-chemical action of light; in other words, 
that all the rays of the spectrum or all colours 
will act on sensitive emulsions if sufficient expos- 
ure be given. The expression most usual now 
is the ‘‘more refrangible”’ or ‘‘less refrangible’”’ 
rays. 

In process work, where the electric arc light is 
almost entirely used, the actinic value of the 
light is ‘of great importance. It is found that 
the enclosed arc is very rich in actinic rays, 
and these are increased by operating the lamps 
with a comparatively high voltage, resulting in 
a long flowing arc emitting a violet light. This 
is photographically very active, and exposures 
are greatly reduced compared with those neces- 
sary with the open arc. 


Actinic Doublet 


ACTINIC DOUBLET 


ACTINIC FOCUS 

A term generally used to express the focus 
for the blue end of the spectrum, to which the 
sensitiveness of the earlier photographic plates 
was almost entirely limited. The focus of the 
yellow or strongly luminous region of the spec- 
trum did not always coincide with that of the 
blue and violet rays, so that an image sharply 
focused, as far as visual observation went, gave 
a blurred image on the sensitive plate. A lens 
giving such a result was said to have the visual 
and ‘“ chemical’ or actinic foci non-coincident. 
This is very rare in modern lenses, even of the 
cheaper class. (See also ‘‘ Lens.’’) 


ACTINOGRAPH 

An instrument for estimating the exposure 
necessary for a photographic plate, invented by 
Hurter and Driffield. It embraces no new 
principle, but is simply a kind of slide-rule for 
atriving at a result without calculation in a 
manner precisely similar to that which was 
adopted in the exposure tables that were pub- 
lished by W. K. Burton and other pioneers 
of modern photography. It consists of two 
parts, a light scale and a scale of subjects, plate 
speeds, and lens apertures. The light scale is 
based on the fact published by Dr. Scott about 
1880 that in clear weather the actinic value of 
the light varies in direct proportion to the height 
of the sun above the horizon. For example, 
the altitude of the sun is nearly four times as 
great in mid-summer as in mid-winter, and little 
more than one-fourth of the exposure is neces- 
sary in the middle of June when compared with 
that of December. In practice its use is less 
satisfactory to the ordinary worker than the 
exposure meter. 


ACTINOMETER 

An instrument for gauging the depth of print- 
ing in those processes in which little or no visible 
image is produced by exposure to light; known 


(See ‘ Lens.’’) 


A. Actinometer with Paper Scale 


also as a print meter. There are two types of 
actinometers, differing both in character and in 
method of using. The essential feature in each, 
however, is that a piece of silver ptinting-out 
paper is exposed to light until a certain effect 
is produced, and by this the correct printing of 
the invisible image can be estimated. The older 


Actinometer 


and simpler pattern consists of a small box with 
an opaque cap or lid, in which is a small opening. 
At one side of this opening is a small square 
painted in a medium dark colour to resemble 
as closely as possible the colour that silver paper 
assumes and passes during printing. It is essen- 


B. Johnson’s Actinometer 


tial that this tint should be a medium tint in 
silver printing, and that the paper should pass 
the colour by continuing the exposure; other- 
wise it would be difficult to determine when the 
correct matching of the colour, or the correct 
time of printing, had been reached. A square 
or a strip of silver printing-out paper is placed 
under the lid and kept in fair contact by a pad. 
The actinometer is put out to print with the 
frames containing the carbon prints, and the 
small portion of the silver paper visible through 
the opening gradually darkens until it matches 
the printed tint at the side of the opening. The 
time necessary for this is called “one tint.’ As 
soon as one tint is printed the silver paper is 
moved forward and a second tint printed, and 
so on until the prints are completed. Experience 
alone can determine how many tints will corre- 
spond with the correct exposure for any print; 
as negatives and actinometers vary considerably. 
With this form of actinometer each succeeding 
tint need not always be exposed immediately 
the preceding one is printed if the light is uniform. 
The time of matching the tint may be noted, and 
three or four succeeding tints timed from that. 
The second form of actinometer is more simple 
in use, and more suitable for the amateur worker, 
It consists of a series of squares of varying density 
—practically a test negative—and is used exactly 
as an ordinary negative. These Squares range 
from one very thin up to a density equal to that 
of the sky in a very strong negative, and they are 
numbered consecutively to facilitate reference 
in printing. If a piece of silver paper is exposed 
to light under this test plate, Ba Hit exposure 
will show a faint image of the first two or three 
Squares, and with a longer exposure more of the 
Squares will be visible on the silver paper. The 
Squares are surrounded by an opaque margin 
to render the image more plainly visible. The 
actinometer is put out to print at the same 
time as the frames containing the carbon prints, 
and each is brought in when the number con- 
sidered correct for that negative is reached on 
the actinometer. The actinometer is examined oc- 
casionally, and the “‘number ”’ that is considered 
printed is the square bearing the highest number 
that can be seen. Of course, a very faint image 
of that square is all that will be visible, the lower 
numbers, that have been fully printed for some 


Actinometric 


time, being seen as darker squares. These darker 
Squares assist in determining the highest number 
visible—the faintest square that can be seen. 
One actinometer will serve for several frames, 
provided that all are put out at the same 
time. 

In process work, various forms of actinometers 
are used for timing the printing of the image on 
the plate when exposed to daylight. The sim- 
plest form is that shown at A, consisting of a 
series of thicknesses of tracing paper bearing a 
number corresponding to the layers underneath. 
Another form has a glass scale bearing a 
Woodbury film, the pigmented gelatine graduat- 
ing in thickness from transparency to opacity. 
Burton’s actinometer consists of a series of six 
tiny negatives made by the carbon process. The 
negative to be printed can be compared with 
these, and a corresponding exposure given. 
This form of actinometer is very useful for collo- 
type and photogravure work. Johnson’s acti- 
nometer B is chiefly used for carbon printing. 
It only registers one tint, which is compared 
with a suitably coloured mask. If more than 
one tint is required to complete an exposure, 
the sensitive paper is shifted to a fresh position. 
The Sanger-Shepherd fraction tint actinometer 
consists of a scale of densities on a quarter-plate 
glass which is put into a printing frame and a 
piece of sensitised paper exposed behind it. It 
is very useful for timing the bichromated films 
in colour transparency work and for carbon 
printing, but it can be applied to any other 
snag in which the exposure has to be accurately 
timed. 


ACTINOMETRIC (Fr., Actinométrique ; Ger. 
A ktinometrisch) 

Pertaining to actinometers, or to the measure- 
ment of the chemical, or actinic, power of light. 
Actinometry is the branch of science that deals 
with the numerous methods of testing the 
chemical activity of light, and which makes a 
study of the variations in its intensity in differ- 
ent quarters of the globe, or at different seasons 
and hours. 


ACTINO-POLYCHROME (Fr., Actino-Poly- 
chrome; Ger., Farbenphotograph) 


An early name for a photograph in natural 
colours. 


ACTION 

More often than not, action is rendered in an 
unsatisfactory manner by photography, although 
this does not apply to cinematograph renderings. 
A person’s mental impression of a man walking, 
a horse running, and so on, is the result of a 
blending of all the different positions assumed 
during the action. A single photograph natur- 
ally records but one position, and inadequately 
suggests the idea of action (see ‘‘ Chromo-photo- 
graphy *’). 

What is known as an “ instantaneous ” picture 
of a railway train or other object in rapid motion 
will not convey the impression of speed if it 
shows, for example, the spokes of the wheels 
sharply defined; rather would it suggest sus- 
pended motion. O. G. Rejlander once well ex- 
emplified this in a couple of photographs of a 
lady at a spinning wheel. In one, the foot and 


Adurol 


spokes were of microscopic sharpness; in the 
other, the foot and wheel were slightly blurred 
by intentional movement. Yet it was the 
second that gave the better impression of an 
“instantaneous ” picture and the more complete 
suggestion of action. 


ADAMANTEAN 


An old form of ferrotype plate, largely used 
for the wet collodion process. 


ADAMANTINE PROCESS 

A secret process of half-tone etching on copper 
invented by A. C. Austin in the United States. 
It produced an extremely hard black enamel 
resist image for etching. Probably it was a 
modification of the fish-glue process, but no 
details have been published. 


ADAPTERS (See “Plate Adapters” and 
“Lens Adapters.’’) 


ADHESIVE TISSUES 

Thin sheets of paper prepared, generally by 
the use of shellac, for use in the dry-mounting 
process, 


ADIACTINIC 
actintsch) 


Non-actinic; a term sometimes applied to the 
red or orange glass and fabric used to screen the 
light in a dark-room, No light, however, is 
absolutely non-actinic, since any light, what- 
ever its colour may be, will affect a photographic 
plate if sufficient time is allowed. Photographs 
have, in fact, been taken by the light obtained 
from a ruby lamp, although the exposure was, 
necessarily, very prolonged. For this reason, 
the plate should not be unduly exposed to the 
light of the lamp when developing, however 
‘*‘safe’’ it is believed to be. The “safety” of 
any so-called non-actinic glass or fabric is merely 
relative, and much depends on the nature of 
the plate or paper and its particular colour- 
sensitiveness. Thus, a yellow fabric or material 
that is quite safe for developing bromide papers 
will instantly fog a rapid dry plate; while even 
a deep ruby light will have a marked effect on 
a panchromatic plate. 


ADIAPHOROUS 
A diaphor) 

Neutral ; a chemical term, sometimes applied 
to substances that are neither acid nor alkaline. 


ADON 

A low-power telephoto lens, especially suit- 
able for hand-camera use. The positive lens is 
placed in front of the ordinary lens of a camera, 
in this way producing an enlarged image without 
abnormal extension of the camera or substantial 
reduction of the working aperture of the lens. 


(Fr., Inactinique; Ger., Un- 


(Br.,. Adtiaphore; . Ger, 


> 


ADUROL (Fr. and Ger., Adurol) 

A developer intermediate in character between 
the short factor developers, such as pyro and 
hydroquinone, and the longer factor developers 
such as metol, rodinal, amidol, etc. ; introduced 
in 1899. It is a mono-chlor (or mono-brom) 
hydroquinone. Adurol-Hauff has the formula 
C,H, Cl(OH),, and Adurol-Schering C;H, Br(OH), 


Adurol 


—their actions being similar. The developer 
as purchased is in the form of a white or greyish- 
white crystalline powder, readily soluble in 
water and alkalis. In its action and results it 
resembles hydroquinone, but it is more soluble, 
keeps better, and the negatives are slightly softer. 
The addition of potassium bromide as a restrainer 
has not much effect, and the developing action 
is not much slower when the solution is cold. 
Since its introduction many formule have been 
published for one-solution, two-solution, and 
three-solution developers. The following are 
those in most general use :— 


Sodium sulphite 8 oz. 400 g 

Potass. carbonate oF) 300 ,, 

Water ‘ n 20, 1,000 ccs, 
Shake till dissolved, then add— 

Adurol I Oz, 100 g. 


For negatives and gaslight paper dilute with 
3 to 5 parts of water; and for bromide prints 
with from 7 to 10 parts of water. 

The above is a one-solution developer, and 
may be used over and over again. The formula 
for the two-solution developer is :— 


No. 1. Adurol , . 85 gers. 17 g. 
Sodium sulphite . 13 oz. Bey. 
Water to OO sis 500 ccs, 

No. 2. Potass. carbonate. 1} ,, 125 g. 

Water to 100 ge 500 ccs. 


For use with plates and gaslight paper mix 
3 parts of No. 1 with 2 parts of No. 2: for 
bromide prints add an equal quantity of water. 


A three-solution adurol developer is as 
follows :— 

No. 1. Sodium sulphite . 650 grs, 130g 
Adurol , . BOL. 16.5 
Water to IO OZ 500 ccs 

No. 2, Sodium carbonate. 100 grs. 20 g. 
Water to 1OZ, 50 ccs 

No. 3. Potass. bromide 48 grs, IO g. 
Water to ee a a 50 ccs, 


For soft negatives mix 1 oz, of No. I, 310 minims 


of No. 2, and 20 minims of No. 3. For more 
brilliant negatives use 10 drms, of No. I, $ Oz. of 
No. 2, and $ drm. of No. 3. The three-solution 
formula is best for time-exposed plates, and when 
over-exposure is suspected. 

Adurol combines well with metol and gives 
a developer which acts like metol-hydroquinone. 
One formula is :— . 


Metol . 


- 130 grs. 13 g. 
Adurol ; . of) 4.2 OZ, 50,, 
Water to . ee eos 1,000 ccs, 
Dissolve and add gradually— 
Sodium sulphite 7 OZ. 350 g. 
Potass. carbonate 43,, 225.4, 


For negatives and gaslight papers, dilute with 
10 times the quantity of water ; for bromide 
prints, with 15 times the quantity of water, 
or take of the stock adurol-metol developer as 
above 1 drm. and sufficient water to make 
2 oz., and add a little bromide. 

Adurol is the best developer for obtaining 
warm tones on bromide paper by direct develop- 
ment. The concentrated one-solution developer 


5<e) 


Aerial Image 


as given above (let it be called A) is used with 
three others—namely, 10 per cent. solutions of 
potassium bromide, B; ammonium bromide, 
C; and ammonium carbonate, D. The colours 
are obtained by altering the exposures and vary- 
ing the proportions of the four solutions, 


ADVERTISING, PHOTOGRAPHY IN 


Photographs are extensively resorted to in 
the production of effective pictorial advertise- 
ments reproduced by the half-tone process. 
They are only occasionally used in the form of 
straight prints, but are nearly always ‘* worked 
up” by skilled artists into what are actually 
monochrome wash drawings. Frequently the 
advertiser wants ideas rather than technically 
good prints, and he has at his command the 
services of men who can work up the poorest 
print until the desired effect is arrived at. So 
much work, in fact, is generally done by the 
artist that the photographer may easily fail to 
recognise the finished picture. A plan frequently 
adopted by the artist is to cut away the back- 
ground, paste as much of the print as required 
on white cardboard, and then “ work up” by 
means of the air-brush, etc., introducing suit- 
able wording, etc. Often only the head is used 
from a photograph of a model, there being always 
a fairly brisk demand for studies of pretty ladies 
and children; but in submitting pictures to 
advertisers care should be taken about copy- 
right matters (see ‘‘ Copyright ”’), aS any error 
on the part of the photographer may possibly 
put the advertiser to much trouble and expense. 
It is courteous, and often necessary, to obtain 
the model’s permission to use his or her photo- 
graph in the proposed manner. Rough prints of 
suitable subjects should be submitted to adver- 
tisers with the intimation that, if desired, 
enlargements will be supplied upon bromide 
paper for working up. More often than not it 
is a waste of time on the photographer's part to 
work up a photograph according to his own 
ideas, and it is better to submit an untouched 
print and to leave the rest to the advertiser's 
artist. 


AERIAL FOG (See “ Fog.’’) 


AERIAL IMAGE (Fr., 
Aetherisch Bild) 


A properly corrected lens produces, as it were, 
an aerial model at its focus of the scene at which 
it is directed. Each portion of this model is at 
the same relative distance from other portions 
as are the corresponding parts in the scene 
itself. Different parts of this aerial model are 
brought into focus on the ground-glass screen 
as the lens is racked in or out, so that the pic- 
ture shown on the screen and recorded by the 
plate may be regarded as a section, vertical to 
the axis of the lens, through the many light rays 
which constitute, or proceed from, the aerial 
model. Owing to the coarse grain of the ground- 
glass screens at first supplied with photographic 
apparatus, it used to be thought that critical 
focusing could only be accomplished when the 
aerial image is directly inspected, which could 
be done by means of a telescope attached to the 
camera and arranged to focus simultaneously 
with it, or by having a transparent spot on the 


Image aérienne ; Ger., 


Aerial Perspective 


focusing screen, made by cementing a micro- 
scopic cover glass on the latter with Canada 
balsam. This idea is theoretically correct for 
obtaining the greatest possible sharpness; but 
general satisfaction is now given by the definition 
obtainable by the ordinary method of focusing, 
especially if finely-ground glass is used. Ground 
glass of quite superior fineness is now procurable 
which, in conjunction with a really good lens, 
should remove most of the difficulties met with 
by earlier workers. An advantage of the tele- 
scope attachment was that it enabled moving 
objects to be followed, with the plate in position 
ready for exposure, a result now achieved more 
conveniently by the use of a reflex camera. 


AERIAL PERSPECTIVE 

A gradual softening down as objects recede 
into the distance, whereby they lose strength 
both in colour and in light and shade. Very 
distant objects are often seen as a mass of light 
grey without detail. A print which success- 
fully renders this is said to possess “ atmo- 
sphere,” and the suggestion of space and air is 
of very great value in pictorial work. The use 
of orthochromatic plates in conjunction with 
deep colour screens frequently destroys aerial 
perspective to a greater or less extent. 


AERIAL PHOTOGRAPHY 

The art of taking photographs from aeroplanes, 
airships, balloons, kites, etc. Very quick expo- 
sures are necessary because of the movement and 
of the great flood of light. Photographs were 
first taken from a balloon by Nadar, of Paris, in 
1858, since when photography from balloons has 
been practised in war time very considerably, 
particularly during the American and South 
African wars. In balloons, airships, etc., the 
operator holds the camera, but in kite work the 
shutter is released by means of a cord held by 
the operator on the ground as explained under 
the heading “‘ Kite Photography,’ where details 
of working will be found. The best photographs 
from balloons are, according to the late Rev. 
J. M. Bacon, those taken at an elevation of 
between 250 ft. and 4,ooo ft. At a greater 
height than 4,000 ft. it ceases to be worth while 
to use the camera, since the particles of water 
and dust suspended in the atmosphere spoil the 
definition and sharpness of the pictures. M. 
Antonin Boulade, the eminent French authority 
on the subject, has advocated orthochromatic 
plates, and those sensitive to rays chiefly 
between the G and F lines. The choice of a 
screen is also of the utmost importance, and 
the best results in his opinion were those obtained 
with a two or three “times” screen. From 
great altitudes, where the action of the blue of 
the sky is very intense, yellow screens needing 
about six times the normal exposure produce 
the best negatives, 


AERIAL SCREEN (Fr., Ecran dairy; Ger., 
Windschirm) 

A form of screen for giving relief and other 
effects for optical lantern pictures, its special 
object being to arrest the light coming from a 
lantern and to reflect it back to the point at 
which the projected image is to be observed. 
The ‘‘ Bruce” aerial screen consists of a white 


II 


Aerial Screen 


lath, turning on a vertical axis in a plane parallel 
with the lantern lens, The mechanism and the 
rotating lath occupy a position in front of a 
black velvet screen or background, which absorbs 
all rays of light not falling on the lath and thus 
prevents them from reaching the eye of the 
observer. An ordinary optical lantern projects 
the subjects, which are preferably pictures of 
statuary in which fine photographic quality is 
present, giving as much rotundity as possible, 
and having a black background. The revolving 
lath, which takes the place of the ordinary lan- 
tern sheet, is caused to rotate at a moderate 
speed, calculated to make one revolution within 
the time needed to satisfy the laws of persist- 
ence of vision. Viewing it in broad daylight as 
it is rotated at the specified speed, it would 
present the appearance of a transparent cylinder. 
When the apartment is darkened and the pic- 
ture is projected upon the rotating lath, the 
subject presents a somewhat solid aspect, and 
the audience will not be conscious of a revolving 
device, the illusion being caused by light from 
all parts of the image impinging upon the lath 
as it arrives at each and all of its positions. In 
virtue of the law of persistence of vision, there- 


4 xD 
1 
what 
i y---* 4 ‘ 


© WAPOA. IERIE Te 


Producing Illusion with Invisible Screen 


fore, a complete image will be made up. The 
chief object of this form of aerial screen is to 
bring about relief, but naturally a full stereo- 
scopic effect is not obtained in this way. Another 
form of aerial screen consists of a column of 
vapour rising from the ground and acting as a 
reflector of the projected rays of light, just as 
a cloud in the sky may reflect the rays of the 
sun, but as the medium cannot be controlled 
as regards its reflecting surface it is only useful 
for producing weird effects in which absolute 
definition is not a necessity. 

Yet another and much more recent form of 
aerial screen is that in which the laws of partial 
reflection are made use of; it is termed “ the 
invisible screen,’? because the medium upon 
which the image is actually received is hidden 
from the observer’s view by the front of the 
proscenium. A method of reflection somewhat 
similar to that used in the old illusion known as 
**Pepper’s Ghost”? is adopted, but there are 
variations in the arrangement of the apparatus 
which make the results far more perfect and 
realistic. An observer situated in the auditorium 
at A (see the illustration) looks towards the pro- 
scenium B, and sees in a clear plate glass c the 
aerial image D E, and at the same time observes 
at F any actors (real persons) who may be 
performing. The light rays constituting the 


Aerograph 


spectre DE are arrested before teaching the 
glass Cc by a semi-transparent screen G. In the 
basement under the stage an ordinary optical 
lantern, or a kinematograph projector H, is set 
up. A mirror J, placed at an angle of 45 deg. 
in relation to the optical axis of the lantern 
objective, diverts the light from its horizontal 
course into a vertical direction, so that the 
defined picture or image is received upon the 
semi-transparent screen Gc. In virtue of the 
angle of reflection being equal to the angle of 
incidence, whatever may be projected on ¢ will 
be seen by the observer at A, and will appear to 
be situated in mid-air in the Vicinity of F. 
Hence, the so-called “ invisible Screen ’’ may be 
regarded as the aerial Screen, although the 
aeriograph is seen in quite a different place. The 
chief object of the invisible screen in this case 
is to afford means for producing aerial images 
or spectra in combination with real actors ; 
whilst by the use at H of a kinematographic 
apparatus instead of an ordinary lantern many 
startling effects, otherwise impossible, are pro- 
duced. 


AEROGRAPH, OR AIR BRUSH 
A évographe ; Ger., Aerograph) 

A mechanical Sprayer working by means of 
compressed air, and used for finishing and work- 
ing up both prints and negatives ; invented by 
Charles L,, Burdick, of Chicago, in 1892, and 
introduced into England a year later. It is 
capable of great technical possibilities, and pro- 


(Pr, 


Aerograph Handpiece 


duces effects varying from peculiarly soft and 
beautiful graduations to strong and vigorous 
work, At will, and in successive instants of time, 
the operator can draw lines or wide bands of 
colour, and shadows, either soft and delicate, or 
hard and coarse. The complete outfit includes the 
handpiece, or fountain air brush, an air pump 
with compressed air reservoir, an air pressure- 
gauge, rubber tubing, liquid colour, etc.: inas- 
much as a high and uniform air pressure is 
essential to the best results, a motor-driven air 
pump is superior to the foot-operated one, and 
both kinds are manufactured. Cylinders of com- 
pressed carbon dioxide (“carbonic acid gas ’’) 
may be used in place of the pump with equal 
convenience. When using the foot pump the 
pressure obtained is about 15 Ib. per Square inch, 
and when using the motor pump from 30 Ib. to 
40 lb. per square inch, this producing a much 
finer grain. 

The illustration shows the appearance of the 
aerograph. Air is pumped into a chamber 
connecting with the handpiece by means of a 
rubber tube at a. Finger pressure on a button B 
opens a valve and admits the air, which sucks 
the liquid colour from the reservoir ¢ and throws 
it from D in the form of a fine spray, over which 
the operator has complete control. ‘The spray 
is regulated and stopped by a needle-like rod E 
worked by B. 


I2 


Aerograph 


In the management of the aerograph, scrupu- 
lous cleanliness is always necessary, Keep the 
pencil in the case when not in use, and before 
fitting it up for service, pump air into the 
cylinder, squeeze the tube for a moment or so, 
and then release so as to allow the dust inside 
the tube to blow out. Use the colour thinly, 
and go over the work several times to get a fine, 
even grain. Use fresh colour for every occa- 
sion, and change the water frequently to avoid 
dust, which otherwise will cause the colour to 
splutter. Before and after using the instrument, 
pass two or three lots of clean water through it, 
and clear away any accumulation of paint with 
a wet brush. To adjust the needle, just fit it 
easily to the platinum point where the valve 
lever is as far forward as it will go. Do not 
jam it hard and push far in, otherwise too much 
colour will be ejected on pressing down the 
valve. Also see that the rubber tubes are free 
from kinks or bands. Having mixed the colour 
in a clean saucer, transfer to the reservoir by 
means of a brush. Spray a little in the air 
before treating the original, to make sure that 
all the cleaning water is expelled and the brush 
is working properly. Hold the aerograph about 
6 in. distant from the original, press the lever 
down and slightly backwards, move it horizon- 
tally with a gliding Sweep from left to right, 
beginning at the top left-hand corner, and 
releasing the valve at the end of each journey 
until it has travelled in this way downwards 
over the whole space to be covered, The air 
brush unaided does not produce sharply defined 
lines and edges; paper masks must therefore 
be used to obtain these, or if the background has 
merely to be painted out, then the parts that are 
to be protected can be covered over with a 
Special preparation, “Masklene,” supplied by 
the makers of the aerograph; the colour is 
sprayed on, and the protected parts are then 
cleaned with a pledget of cotton wool soaked 
in benzine. 

In process work, the aerograph is extensively 
employed for working up originals for repro- 
duction, ae photographs of objects for 
catalogue illustration, Backgrounds are in most 
cases put in with the aerograph and vignetted 
off. Sometimes the main object is cut out of 
the photographic print with scissors or a sharp 
knife, then mounted on cardboard, and a back- 
ground and other detail put in. Another 
method largely adopted is to stop out portions 
on which the aerograph Spray is not to be 
applied, the stopping-out medium being of such 
a nature that it can afterwards be removed with- 
out injuring the rest of the drawing. . The 
medium used may be either of a gteasy nature, 
such as vaseline, which may be afterwards 
cleared away with benzol, or it may be a cellu- 
loid varnish, which may be removed with amyl 
acetate or other solvent of celluloid. India- 
rubber solution and yolk of egg are other sub- 
stances used for the same purpose. The former 
can be peeled off by rubbing with the ball of the 
finger, whilst the latter will flake off. In either 
case the colour applied by the aerograph comes 
away with the medium, and leaves quite clean 
the portions which have been covered. Larger 
surfaces may be stopped out by cutting out 
masks of tracing paper and attaching these 


Aerometer 


temporarily to the print with rubber solution. 
The colours used should be mixed to match as 
nearly as possible the tints of the original to be 
worked up. Chinese white should be avoided, 
as it photographs darker than the white papers 
on whichitis applied. Albanine, Ullmanine, and 
Blane d’Argent are good whites to use for this 
work. Lampblack and “process black’ are 
the blacks commonly employed. For large 
lithographic work, such as posters, a larger hand- 
piece is employed, which will give a coarser spray 
and will not clog with the transfer ink necessi- 
tated by the lithographic process. 


AEROMETER 


A hydrometer for measuring the density of 
acids. 


AESCULIN (Fr., 
Schillerstoff) 
Synonyms, esculine, esculin, esculinic acid, 
polychrome, bicolorin, enallachrom. An ex- 
tract obtained from the bark of the horse- 
chestnut (4#sculus Hippocastanum). C,;Hy,O,. 
Molecular weight, 340. A white powder, a 
solution of which, of astrength of about 1 part 
in 500 parts of water, is used as a filter to 
absorb ultra violet rays. 

In process work, where the white (particularly 
Chinese white) reproduces as if it were yellow, 
an zsculin filter should be used. This may be 
a solution contained in a glass cell having parallel 
sides, or it may be in the form of a dry filter. 


AGAR-AGAR, OR AGAL-AGAL (Malayan) 
(Fr. and Ger., Agar-agar) 

A gelatinous vegetable material obtained from 
certain white seaweeds (Gracilaria lichenotdes 
and Eucheuma spinosum), found principally on 
the shores of the Red Sea. It is used to a small 
extent as a substitute for gelatine in plate and 
paper making, but it is more difficult to melt 
than gelatine, and is not generally so satis- 
factory for emulsion work. It has also been 
recommended as a substitute for arrowroot in 
the preparation of silver paper, the latter, if 
very porous, being first sized with a 1} per cent. 
solution of gelatine. Five parts of agar-agar 
are allowed to soak for an hour or two in 
500 parts of water, heated till dissolved, boiled 
for five minutes, and then mixed with twenty 
parts of common salt and strained through a 
cloth. It is carefully brushed on the paper, and 
this, when dry, is floated in the dark upon a 
14 per cent. solution of silver nitrate containing 
Io per cent. of citric acid. In the case of thick 
and coarse paper, the silver solution is first 
brushed on, and then, when dry, the paper is 
floated on the agar-agar solution and again dried 
in the dark. After being sensitised the paper 
keeps well. It is printed and toned as other 
plain silver papers, but if platinum is used as a 
toner the picture must be deeply printed. 

In process work, agar-agar has been suggested 
as a substitute for fish glue in the enamel pro- 
cess of preparing the resist for etching, but it 
has not come into commercial use. 


AGATE BURNISHER 
A burnisher consisting of a polished piece of 
agate fitted to a handle; it was used in the 


fisculine ; Ger., Askulin, 


13 


Albert’s Colour Process 


original method of burnishing albumen prints. 
The unmounted print was laid on plate glass or 
marble and polished with the burnisher. The 
operation was thought to cure ‘‘measles’’ on 
prints, and give depth to the shadows. ‘The 
ptocess was rendered obsolete by the intro- 
duction of the burnishing machine. 


AIR-BELLS (See ‘‘ Bubbles,’’) 
AiR BRUSH (See ‘“ Aerograph.’’) 
AIROSTYLE 


A form of air brush, introduced in 1907. 


AKTINAL (Fr., Actinal) 


A preparation sold in Germany as a desensi- 
tiser for exposed plates, after treatment with 
which they may safely be developed in daylight, 
using a metol-hydroquinone developer, with 
caustic potash as the accelerator, and fully 
restrained with potassium bromide. It is said 
to be a 4 per cent. solution of potassium iodide. 


ALABASTER, OR ALABASTRINE, PRO- 
CESS 

A very old process for improving the quality 
of positives made on glass by the wet collodion 
ptocess. ‘The picture was bleached in a solution 
of mercuric chloride in order to increase the 
brilliancy of the white image, was then varnished, 
and finally, when dry, was bound at the back. 
The process is even now occasionally used in 
obtaining a good result from a thin gelatine 
negative, which must be free from fog. The 
faulty negative is bleached in a solution of mer- 
curic chloride, washed, dried, backed with black 
material, and copied in the camera. Ready- 
made mercury solutions for the process have 
been sold under the name of “‘ alabaster ’’ solu- 
tions. The original formula is: Water, 2 oz. ; 
nitric acid, 60 minims; hydrochloric acid, 60 
minims; to which must be added sufficient 
mercuric chloride to saturate the solution, 
the excess remaining in crystals; finally, 60 
minims of alcohol must be added. A more 
modern mixture—and one equally suitable for 
dry (gelatine) plates—is : Water, 2 oz. ; bichloride 
of mercury, 40 grs.; hydrochloric acid, 1 drm. ; 
sodium chloride (common salt), 20 grs.; and 
sulphate of iron, 20 grs. Wet collodion pictures 
bleached with this are permanent if varnished, 
and so protected from the atmosphere, but dry 
plate negatives thus bleached will not remain 
white for long if kept in a strong light. 


ALBANINE 

A very pure white water-colour pigment used 
by process retouchers for working up originals 
either by brush or with the aerograph. It 
photographs as white, and should be employed 
pure for brilliant touches in the highest lights 
of a drawing or print. It can be mixed with 
‘*‘ process black ’’ for obtaining graduations of 
shadow. No other white should be mixed withit. 


ALBERINI’S PROCESS (See “ Asphaltum.”’) 
ALBERT PAPER (See ‘“ Photo-Lithography.’’) 


ALBERT’S COLOUR PROCESS (See ‘‘ Cito- 
chrome.’’) 


Albert’s Relief 


ALBERT’S RELIEF OR GALVANO PRO- 
CESS (Fr., Méthode a vehaussey d’ Albert ; 
Ger., Albert’s Unterlage) 

A method of imparting a varying relief to the 
surface of printing blocks, so as to avoid the 
necessity for overlaying to bring up the darker 
portions in typographic printing; invented by 
Dr. E. Albert, of Munich. A heavily inked 
proof is taken from the plate, and transferred 
to a thin zinc plate. The ink image is strength- 
ened by dusting with resin or bitumen powder 
and heated to fuse the powder and ink. Then 
the plate is etched strongly until the highest 
lights are etched away, and the half-tones 
partially, the shadows remaining solid and, con- 
sequently, in the highest relief. This plate is 
covered with a sheet of thin gutta-percha, and 
the back of the original: plate placed on it in 
exact register, the whole being then put into a 
heated press, with a soft packing over the face 
of the plate. On strong pressure being applied 
the underlay plate is attached to the original 
plate, and the undulations of surface on the 
former communicate relief to the latter plate. 
The combined plate is mounted on wood or 
metal to type height, and is then ready for 
printing, no “‘making-ready”’ by the printer 
being necessary. 


ALBERTYPE, ALBERT-TYPE, OR ALBERT- 
OTYPE (Fr. and Ger., Albertypie) 

The first workable collotype process made 
known; invented by Josef Albert, of Munich. 
It differs somewhat from the present-day collo- 
type process. A piece of glass 3 in. thick is 
coated, in a dark-room, with the following solu- 
tion :— 


Water ° . . 300 parts. 
Albumen . : - 550045 
Gelatine ° : WS ters 
Potassium bichromate 8 


” 


When the film is dry it is exposed to light for 
two hours through the glass, backed by a piece of 
dark cloth, so that the film may harden from 
the bottom (next the glass) to the surface. The 
exposed plate is now coated with the following :— 


Gelatine ; ; 300 parts, 
Potassium bichromate top 2s. 
Water F - 1,800 


o> 


When again sufficiently dry the plate is exposed 
trom the coated side under a negative, and is 
then washed for fifteen minutes, and dried. 
‘The film is next damped, and inked in the usual 
way. Printing is done in a lithographic press, 
or in a proper collotype press. The process is 
said to give prints with fine half-tones, but it 
requires considerable care and experience in 
manipulation, much depending on the printing. 


ALBUM (Fr. and Ger., Album) 


Blank-leaved books for storing and display- 
ing photographic prints. They may be roughly 
divided into two classes—slip-in and _paste- 
down. As the names suggest, the former has a 
double page with cut-out openings on the upper 
leaf so that the prints (generally glazed) may be 
slipped in between the two sheets; the latter 
has plain pages on to which the prints are pasted. 
The colour of the leaves is important; white is 


14 


Albumen 


generally unsuitable, and bright tints should be 
avoided. It is also important when prints are 
to be pasted down to make sure that both paper 
and adhesive are free from acid or anything that 
will be deleterious to the photographs. Prints 
do not show to the best advantage when many 
are crowded together on one page. A print 
that is worth mounting at all deserves to be 
presented alone on a separate page, of a tint 
that is harmonious and unobtrusive. Special 
albums are made for the storage of film nega- 
tives, thus affording an easy means of indexing 
and reference. 


ALBUMEN (Fr., Albumine; Ger., Albumen) 


A very complex organic compound containing 
carbon, hydrogen, oxygen, and sulphur, which 
occurs both in the animal and vegetable kingdom. 
Animal albumen exists as the serum or white 
fluid of blood, but photographically the white 
of eggs is the only animal albumen used. To 
prepare it for photographic purposes the whites 
of eggs should be separated from the yolks and 
the germ, and thoroughly beaten to a froth, 
allowed to settle for twelve or twenty-four hours, 
and then filtered. Actually, the albumen is 
contained in minute cells, and the beating has 
the purpose of breaking the cell walls, which 
subsequently form the flocks or scum. 

Albumen is coagulated by heat (150° F. or 
65°5° C.), by alcohol, and most metallic and 
inorganic salts, the resultant precipitate with 
the latter being albumenates. It is an almost 
colourless, gummy liquid, which dries to a pale 
yellow solid. Seventy grains of the dried egg 
albumen dissolved in one fluid ounce of distilled 
water forms a solution equal to the fresh white 
of egg. The solution is extremely liable to 
decomposition, and should be either freshly pre- 
pared or preserved with an antiseptic. It is 
used for albumenised paper, the albumen nega- 
tive, beer, and positive processes. 

Invert albumen is obtained from ordinary 


albumen by first treating with acid and then 


with alkali, by which treatment it is so altered 
in character that it becomes soluble in alcohol. 
The following process has been suggested by 
Sanger Shepherd :— 


White of eggs 
Glacial acetic acid . 


20 OZ. 
148 mins: 


1,000 ccs. 
16°5 3? 


Beat up thoroughly, and allow to stand for one 
hour, then add a 20 per cent. solution of sodium 
hydrate drop by drop with constant stirring till 
the mixture thickens; next allow to stand for 
one hour, break up into small pieces, and wash 
(see “Emulsion ’’), drain well, and dissolve in 
boiling alcohol. Invert albumen gives an 
extremely tough, structureless film, and was 
suggested for making colour filters. 

In process work, albumen is used as a sub- 
stratum, or for edging the glass plates in making 
wet plate negatives. Also, it is almost univers- 
ally employed with potassium bichromate for 
Sensitising the zine plate for photo-etching. 
Albumen is also often mixed with fish-glue in 
making up the enamel solution for printing on 
zinc or copper from half-tone negatives. Dried 
albumen is frequently employed in preference 
to the liquid white of eggs. Varying opinions 
are expressed as to the quantity of dried albumen 


Albumen Process 


required to equal the albumen of one egg, but 
70 grs, to 1 oz. of water may be taken as a safe 
standard. 


ALBUMEN PROCESS 

NEGATIVES.—An old process invented by 
Niepce de St. Victor, in 1848. Glass was 
coated with albumen containing potassium 
iodide, and the film was sensitised by dipping 
in a nitrate of silver bath. Many modifica- 
tions followed, but probably the process most 
widely used was the one published on May 21, 
1855, by Mayall; this comprised six distinct 
operations, as follow :— 

(1) The albumen (white) of a fresh egg is 
beaten to a snow-like mass with a bunch of 
quills, afterwards dropping into it 10 drops of 
a saturated solution of potassium iodide and 
allowing to stand six hours at a temperature of 
60° F. (2) A piece of plate glass having smooth 
edges is cleaned by rubbing over it nitric acid 
with cotton wool, and polished with Tripoli 
powder moistened with a few drops of a concen- 
trated solution of potassium carbonate. To the 
centre of the back of the glass is attached a 
pneumatic holder to serve as a handle. (3) The 
prepared albumen is strained through linen, and 
is then used to coat the polished side of the glass, 
this being placed on a level slab in a warm and 
dustless place to dry. The glass is now known 
as the “iodo-albumenised”’ glass, and it will 
keep in a good condition for any length of time. 
It may be prepared in daylight. (4) The sensi- 
tising mixture, or “ exciting solution,’’ is made 
by dissolving 50 gers. of silver nitrate in a mix- 
ture of 1 oz. of distilled water and 120 minims 
of strong acetic acid, which operation and the 
following one must be done in a weak yellow 
light. Pour the sensitising mixture into a clean 
porcelain dish a little larger than the plate to 
be coated; place one end of the albumenised 
glass in the solution; with a quill, support the 
upper end of the glass and let it fall suddenly 
into the solution, lifting it up and down for ten 
seconds; take it out, and place it face upwards 
in another dish half filled with distilled water ; 
allow the water to pass over the surface twice, 
take out and set aside in the dark to drain and 
dry. The plate at this stage is ready for expo- 
sure in the camera, and will keep good for ten 
days if kept from the light, in a moderately 
warm place, and free from moisture. The sur- 
plus sensitising solution may be filtered back 
into a black bottle for use again and again, 
adding occasionally a few drops of acetic acid 
and keeping in the dark. Exposure varies from 
four to ten minutes, according to light and stop. 
On a very bright day, and using the f/16 stop, 
Mayall recommended an exposure of five min- 
utes. (5) For development, the glassis placed 
film side upwards on a levelling stand, and a 
concentrated solution of gallic acid is poured 
over it; the image takes from thirty minutes to 
two hours to develop. A temperature of 10° 
higher than that of the room is advised, and 
if the image is feeble the plate is rinsed and 
covered with a solution of equal quantities of 
aceto-nitrate of silver and gallic acid diluted 
with water to half strength. This causes the 
image to appear more quickly and stronger. The 
plate is next washed in three waters, and is 


15 


Albumen Process 


then ready for fixing. (6) The fixing solution 
is made by dissolving 3 drms. of hyposulphite 
of soda in 1 oz. of water. The plate is allowed 
to remain until all the yellow iodide has dis- 
appeared, and is next well washed and dried. 
** Success,’ said Mayall, when publishing this 
process in the Atheneum (No. 1,220), “‘is sure 
to attend anyone practising this method, pro- 
vided the eggs are fresh and the glass quite 
clea1; if the glass is not clean and the eggs 
stale, the albumen will split off the plate during 
the fixing.” Among the modifications which 
followed for the purpose of quickening the plates 
were the addition of grape sugar, honey, and 
potassium fluoride, the latter proving to be the 
best of all. Malone’s and other processes in use 
in the ’fifties of the nineteenth century differed 
in detail from the above, but in essentials were 
the same. 

PosITIvVES.—At one time the albumen pro- 
cess was widely used for the production of posi- 
tives or lantern slides, and even at the present 
time, owing to the exquisite results obtainable 
with it, the albumen process is used by some 
of the largest lantern and stereoscopic trans- 
parency firms in the world. It is hardly a pro- 
cess for the beginner, because of the somewhat 
complicated formule and manipulations. The 
famous “ Ferrier et Soulier”’ slides were pro- 
duced by the albumen process, but the exact 
formula used was kept secret. Other formule 
have, however, been published and worked 
successfully, the best being that in which the 
plate is coated first with collodion and then with 
iodised albumen; the details are as follow: 
Pieces of good clear glass should be thoroughly 
cleaned by washing in a solution of 8 oz. of 
soda in 1 gal. of hot water, and rubbing well 
with rags tied to a wooden stick. Next, the 
plates are rinsed in plain water and placed 
in dilute hydrochloric acid (1 in 20). A sub- 
stratum is next required, and this is made 
by mixing the white of one egg with 50 oz. 
of water; the mixture being shaken up three or 
four times during the day and allowed to stand 
all one night, it is then filtered through fine 
muslin. The plates are taken from the acid 
bath, rinsed, drained slightly, and coated on one 
side with the albumen substratum mixture; , 
next they are laid flat and dried. Great care 
is necessary to avoid dust and to get an even 
coating. When dry, collodionising and sensi- 
tising may take place. Some ready-made 
iodised collodion is obtained (the longer it has 
been iodised the better), and the followirg 
solution is prepared :— 


Distilled water . . 2002 1,000 ccs. 
Silver nitrate . Pye DER 100 g. 
Potass. iodide . +. 2 SiS. eae 


Shake well, stand in sunlight for a day, ana 
filter into a glass dipping bath, when it is ready 
for use. The following albumen solution must 
also be prepared and kept ready at hand for use 
after collodionising :— 

Albumen (fresh white of 


egg) ‘ : to ne 800 ccs 
Liquor ammoniz 2 drms. 26... 
Potass. bromide 10 grs. ah 
Potass. iodide co, ; 2. 
Distilled water 3 0Z 300 ccs 


Albumen Process 


The albumen must be well beaten up with a 
silver fork, the bromide and iodide mixed with 
it, the water and the liquor ammonie being then 
added. The mixture should stand twenty-four 
hours. before use, and then be filtered through 
muslin. Take one of the plates prepared with 
the .substratum, coat with the iodised : collo- 
dion, drain, and move to and fro in the air so 
that .the ether; may evaporate, place at once 
upon the dipper and immerse. in the silver 
nitrate bath. ~ A deep ruby light is not neces- 
sary, an orange or a deep yellow light being 
quite safe enough. The plate must be moved 
up and down in the silver bath a few times, 
allowed to stand for two minutes, taken out, the 
silver drained off, and then washed for a few 
minutes and drained, but not dried. While the 
surface is still damp the plate is covered with 
the albumen solution, drained, and again coated 
with the albumen. When dry, the plate must 
be treated in order to make the bromo-iodised 
albumen more sensitive to light, for which pur- 
pose the following bath is used :— 


Silver nitrate (recrys- 


tallised) . ; . 600 gts, ° 60 g. 
Distilled water to SO OZ. 1,000 ccs. 
Glacial acetic acid . 110 drms. T.cc: 


The plates are allowed to remain in this bath 
for two or three minutes, washed well, and 
flowed over with a nearly saturated solution of 
gallic acid, and finally dried in a warm dark 
place. The plates are then ready for exposing. 
The time of exposure will be about fifteen times 
as long as an ordinary modern gelatine lantern 


plate. Over- is better than under-exposure. 
The following pyro developer should be used :— 
A. Pyrogallic acid . 96 grs. 100 g. 
‘Alcohol to . I OZ. 500 ces. 
B. Potass. bromide . 12 grs. 125 g. 
Water to 1:0z, 500 ccs, 
Cc. Ammonium carbon- 
ate*., . 80 grs, 84 g. 
Water to I OZ, 500 ccs, 


To prepare the developer for use, 12 drops of 
A are mixed with 1 dram of B and 6 drams of C. 
The image soon appears, but will be thin and 
usually requires to be strengthened by redevelop- 
ment, which is-done by applying a small quantity 
of the following developer, after washing off the 
first developer.:— 


Pyrogallic acid . 6 gts. Ae 
Distilled water to =.02, - 85° ccs. 
Citric acid .° 1} grs. I g. 


Before using this, add a few drops of a solution 
of 30 gts. of silver nitrate in 1 oz. of water. As 
soon as dense enough, the plate is fixed in a 
solution of sodium hyposulphite (4 0z. to 20 oz. 
of water); washed for about five minutes, and 
dried.: 
Mary: other formule have been advocated, 
some much more simple than the above and 
witbout ‘the use of collodion, but the process 
described probably gives the most satisfactory 
results and offers fewer opportunities for failure. 


ALBUMEN PROCESS (BEER) 
A dry collodion process for solar photography, 
introduced by Sir William Abney in 1874, also 


16 


Albumenised Paper 


of use for landscape work. Abney’s formula 
is :— 


Alcohol (825) . 44-3 drms. 270-180 ccs. 
Ether 34-5 ,, 210-300 ,, 
Pyroxyline 7 grs. 7 

‘ Ammonium iodide 20s 2" 
Cadmium bromide yar oe 


The relative proportions of alcohol and ether 
ate adjusted according to temperature. The 
plate is then sensitised in a silver bath of from 
40 to 60 grs. per oz., and is next washed, and the 
first preservative applied :— 


Albumen . £02, 100 ccs 
Water; : Rk he | 100: %: 
Liquor ammoniz. ace i toe 


This is beaten to a froth and allowed to settle. 
The clear part is mixed with an equal quantity 
of flat beer or stout immediately before use, 
and is then applied to the plate; fresh bottled 
beer’ or stout must not be used. The excess is 
then drained off, the film washed for two min- 
utes, and finally covered with a solution made 
by adding to every ounce of plain beer 2 grs. of 
pytogallic acid. The plate is then dried in the 
usual way. Great latitude in exposure is per- 
missible, even up to twenty times the correct 
amount, and, if desired, the plates need not be 
developed for a month, but they need to be 


washed just previous to development. For 
developing, four solutions are necessary :— 
A. Pyrogallic acid . 12 gers. 12. 2: 
Water . . I OZ. 500 ccs. 
B. Liquor. ammonie , 
(:880) 1 drm. 62 ccs. 
Water. «See j BHEOU i; 
C. Citric acid . 60 gts. 60 g. 
Acetic acid . . 30 mins, 2 ces. 
Water . I OZ.. 500. ,, 
D. Silver nitrate, - 20 gts. r* 20 oe. 
Water, distilled... 1.0z.. 500 ccs. 


Three drops of B are mixed with each half-ounce 
of A, and flowed over the plate. .-The image will 
then gradually appear. Two more drops of B 
per half-ounce are added, the solution again 
flowed over the plate and returned to the meas- 
ure. Six drops of C are placed in a measure, and 
the partially used developer poured on to it, 
afterwards adding a few drops of D.. The appli- 
cation of -this solution intensifies the image. 
Abney states that it is not advisable to bring 
out too much’ detail with the pyro-ammonia 
solution, but to allow some of it to be brought 
up at the finish with the intensifier. When the 
image is sufficiently dense, the plate is fixed 
either by_a solution of potassium cyanide or 
with “‘hypo,”’ then washed and dried.. The pro- 
cess is*not an-easy one, and many failures are 
likely to be met with, but the resultant negatives, 
when all goes well, are of a ‘remarkably high 
quality. . 


ALBUMEN PROCESS (PHOTO-MECHANIe 
CAL). (See “‘ Zine Etching.’’) ' 


ALBUMENISED PAPER 

A prepared paper for obtaining prints from 
negatives. It is similar to plain salted paper, 
except that albumen is used with the first or 
salting solution in order to give the paper a gloss 


PORTRAIT OF A. HADDON BY FURLEY LEWIS, F.R.P.S. 
STUDIO PORTRAITURE 


Alcohol 


and to keep the silver sensitising solution on 
the surface. The introduction of albumenised 
paper has been credited to Talbot, but definite 
instructions for making it emanated from other 
experimenters—notably Le Gray, Hunt, and 
Pollock—during the years 1851, 1852, and 1853. 
For about forty years albumen paper remained 
the most popular of all printing processes, and 
reigned supreme until the introduction of gela- 
tino-chloride (P.O.P.) and similar papers. It, 
however, is still used by some professional 
workers and for some special processes, as 
crystoleum work, for example. Ordinary white 
papers were used at first, but in 1863 methods of 
slightly tinting the papers mauve, pink, etc., 
by means of dyes, were introduced. 


ALCOHOL (Fr., Alcool; Ger., Alkohol) 


Chemically, alcohols are neutral compounds 
formed by the replacement of hydroxyl OH 
for one atom of hydrogen in a saturated carbon 
compound; for instance, C,H, ethylene gives 
C,H; OH ethyl hydrate, or ordinary alcohol. 
They unite with acids with elimination of water 
to form ethers. Alcohols are hydrates of organic 
radicles and may be considered as equivalent 
in organic chemistry to the metallic hydrates 
in inorganic. For example, KOH potassium 
hydrate; C,H; OH ethyl hydrate. They are 
divided into monatomic, diatomic, triatomic, 
etc., according to the number of OH groups 
attached to the organic radicle. 


Alcohol, Ethyl (Fr., Alcool ordinaire, Alcool 

éthylique ; Ger., Aethylalkohol) 

Synonyms, ethylic alcohol, ethyl hydrate. 
C,H, HO. Molecular weight, 46. Solubilities, 
miscible with water and ether in all proportions. 
A colourless, volatile, inflammable lquid of 
pleasant odour; it is obtained from grain, 
starch, or sugar by fermentation and subsequent 
distillation. Itis principally used for preparing 
collodion (which see). 

Absolute Alcohol contains from 98 to 99 per 
cent. of pure alcohol, and is used for making 
collodion. 

Rectified spirit or spirits of wine contains 
Io per cent.of water, and is known as 58 over- 
proof. The term ‘proof spirit’’ refers to an 
old test with gunpowder, which was moistened 
with the spirit and then a light applied; if the 
gunpowder fired the spirit was termed proof. 


Alcohol, Methyl or Methylic (Fr., Alcool 
méthyliquve ; Ger., Methylalkohol, Holz- 
geist) 


Synonyms, wood alcohol, wood spirit, wood 
‘naphtha, methyl hydrate or hydroxide. CH, OH. 
Molecular weight, 32. Solubilities, miscible with 
water, alcohol, and ether in all proportions, A 
colourless, mobile liquid, prepared by the de- 
structive distillation of wood. It is an excel- 
lent solvent for resins and pyroxyline, with 
which it gives a very tenacious film. 


Alcohol, Methylated (Fr., <Alcool dénaturé ; 
Ger., Brennspiritus) 

Synonyms, methylated spirit, denatured 
alcohol or spirit. Solubilities, miscible with 
water and ether in all proportions. It usually 
contains about 90 per cent. of aqueous ethyl 
alcohol with about 10 per cent. of methy1 alcohol 
and 4 of 1 per cent. of mineral naphtha to render 

2 


17 


Aldehyde 


it unpotable. Industrial methylated spirit does 
not contain naphtha, and can only be obtained 
by special permit of the Inland Revenue under 
a heavy bond; it may be used for nearly all 
photographic purposes instead of pure alcohol, 
except for printing-out collodion emulsions. The 
admixture of methylated spirit with water turns 
it milky in consequence of the separation of the 
naphtha. 

In process work, alcohol plays an important 
part. For making up collodion for the wet 
plate process, absolute alcohol of -805 sp. g. 
is usually employed. Spirit of wine is used 
in the wet plate developer to overcome the 
repellent actions of the silver solution on 
the plate when the bath has become charged 
with alcohol through the frequent sensitising of 
plates. As the bath gets older the proportion 
of alcohol is increased. Methylated spirit is not 
generally employed on account of the presence 
in it of mineral naphtha, which is apt to give 
fog, scum, and other troubles, but industrial 
alcohol (wood spirit) may replace the pure 
spirit on the score of economy. In making up 
collodion emulsion only pure alcohol should be 
employed. Alcoholic solutions of dyes are 
largely used in colour sensitising, and in this 
case only pure alcohol should be used. Methyl- 
ated spirit is used for drying off the fish-glue 
print after development. It is also employed for 
developing resinous images, for making up acid 
resist varnish, for diluting stopping-out varnish, 
and for cleaning off varnish coatings. In the 
aquatint process alcohol is used with resin to 
give the granular ground which is formed on 
the plate for etching. Similarly, alcohol is used 
in certain bitumen processes, such as the Frey 
process, where the alcohol with the asphalt 
causes the film to reticulate—that is, to form a 
network. An alcoholic solution of bichromate 
is used for sensitising carbon tissue, the object 
being to promote quicker drying. 


ALCOHOLOMETER (Fr., Alcoolmétre ; Ger., 
Alkoholometer) 


A hydrometer graduated so that the percentage 
of alcohol can be read off directly on the scale. 


ALDEHYDE (Fr., Aldéhyde ordinaive ; Ger., 
Aldehyd) 

Synonyms, acetaldehyde, ethaldehyde, acetic 
aldehyde. CH, CHO. Molecular weight, 58. 
Solubilities, miscible in all proportions with 
water, alcohol, and ether. A colourless, light, 
inflammable liquid, with pungent smell, ob- 
tained by oxidising ethyl alcohol with chromic 
acid. It was suggested by Lumiére and 
Seyewetz as a substitute for the alkaline 
caustics and carbonates in developers, but it 
is rarely used. It forms, as does acetone (which 
see), compounds with the bisulphites, and its 
action in developers may be represented by the 
same equation. 

In process work, aldehyde as an impurity in 
alcohol is often the cause of foggy negatives in 
wet collodion and collodion emulsion. The 
aldehyde may be detected by adding a small 
quantity of a strong solution of silver nitrate 
to the alcohol and exposing the whole to light 
for some hours, when the liquid will gradually 
blacken if aldehyde is present. 


Alethoscope 


ALETHOSCOPE 
Alethoskop) 


An optical device invented by Signor Ponti, 
of Venice, and intended for the inspection of 
transparencies or ordinary photographic prints. 
It consisted of a large single lens, suitably 
mounted, somewhat after the manner of the 
modern lanternoscope or pantoscope used for 
viewing lantern slides. It was claimed that the 
alethoscope showed single photographs with 
stereoscopic relief, but that is a theoretical 
impossibility, although it is possible to obtain 
a deceptive approximation to relief when looking 
with both eyes through a large convex lens at a 
single photograph, provided the lighting, model- 
ling, and perspective of the picture are good and 
natural; but this effect is more due to imagina- 
tion and suggestion than anything else. If a 
coloured picture is used the illusion is heightened. 
According to Sir Howard Grubb, who investigated 
this effect as seen in the graphoscope, this is 
due to the lens being non-achromatic, so that 
it fringes everything with red on one side and 
with blue on the other. Thus the outline of, 
say, a red flower is a little extended on one side 
to the right eye and on the other side to the 
left eye, which causes the two pictures seen by 
the respective eyes to be really dissimilar, in 
such a manner as to give the appearance of relief 
when combined, although not properly stereo- 
scopic. | 


ALGRAPHY 

A process of lithographic printing from alu- 
minium plates, as a substitute for lithographic 
stone, patented by Joseph Scholz, of Mainz, 
Germany. Aluminium had previously been used 
for lithographic printing, but Scholz was the 
first to make it a commercial process. His 
method chiefly relates to the preparation of the 
surface, phosphoric acid playing an important 
part in the process. 


ALIZARINE, ARTIFICIAL (Fr., Alizarine 
artificielle ; Ger., Alizavin kiinstitch) 

Synonym, dioxyanthraquinone oa—fs. A 
group of organic dye-stuffs obtained from 
anthracene. The only one of importance is 
alizarin S, the sodium-bisulphite compound, 
which has been occasionally used for sensitising 
plates for red. Its action is somewhat uncer- 
tain, and it has been entirely replaced by the 
isocyanines (which see). 


ALIZARINE, NATURAL (Fr., Altzarine 
naturelle; Ger., Alizarin natirlich) 
Synonyms, madder, rubia. The root of rubia 
tinctorum, obtained from South Europe and the 
Orient, yields by extraction the colouring matter 
alizarine, which is used for making carbon 
tissue and in dyeing. 


ALKALI (Fr., Alcali ; Ger., Alkalt) 


The direct opposite to an acid. A term by 
which the accelerator used in development is 
often known. An alkaline solution is one that 
will turn red litmus paper blue, or change the 
yellow colour of turmeric paper to brown. Most 
of the modern developers for dry plates are 
known as alkaline developers because of an 
alkali—ammonia, soda, etc.—being used as the 


(Fr.,  <Aléthoscope; Ger., 


18 


Alkalis 


accelerator. In 1862 a Mr. Leahy, of Dublin, 
found that liquor ammonie assisted the pyro 
developer, but Major Russell, the inventor of 
the tannin process, had for some time been 
experimenting in the same direction, and in 
1862 published the first complete account of a 
workable system of alkaline development. Since 
then alkalis other than ammonia—namely, 
sodium and potassium carbonates—have come 
into wide use. Previous to 1862 ammonia was 
largely used in America, but not in the de- 
veloper itself; the plates were merely exposed 
to the fumes of ammonia before the pyro was 
applied. 


ALKALIS, CAUSTIC 


Potassium hydrate, sodium hydrate, and 
lithium hydrate are examples of the caustic 
alkalis, being often referred to, respectively, 
as caustic potash, caustic soda, and caustic 
lithia. Their caustic nature is easily demon- 
strated by the rapidity with which they will 
disintegrate the human skin. The carbonates 
are sometimes referred to as the “mild” 
alkalis to distinguish them from the hydrates 
or “caustic” alkalis. Caustic soda is, as a 
rule, purer than caustic potash, but both have 
an action upon glass, and render grease soluble 
in water. (See also ‘‘ Caustic.’’) 


ALKALIS, CHEMICAL EQUIVALENCE OF 

All alkalis are not alike in their action as 
accelerators in developers, and one cannot be 
used in the place of another indiscriminately. 
The table below, compiled by George HE. 
Brown, is the most widely used for finding the 
equivalent values of the alkalis :— 


Ss _ = 

8s 83 A 2g 2 
25| $3 | 83 S| sis] 338 | 23 
TURCOM CERISE TUE ab is 
S| S* | 38 | 62) Oats eae 
80 | 112 | 97*14 | 106 286 138 174 
I | 1°400 | *867 | 1°325 | 3°575 | 1°725 | 2°174 
“714 I I*2ig 946 | 2°553 | 1°232 | 1°554 
*834] 1°153 I I‘OQI | 2°944 | 1°42I | 1°791 
-9eS FOSS SOIG I 2°698 | 1°302 | 1°641 
280} °392 340 371 I *483 | °608 
°S80| "812 704 | °768 | 2:072 I 1*260 
*460| 644] °558| *609|1°644| °*793} I 


The ammonia solution (-880) should be weighed, 
not measured. To find weights of other alkalis 
equivalent to any particular compound, run the 
finger down the proper column until the figure 1 
is reached. The figures in the same horizontal 
line are the equivalent weights of the other alka- 
lis as denoted at the head of each column. 
Thus, 1 gr. of carbonate of soda (crystals) equals 
-280 grs. caustic soda or ‘608 grs. potassium car- 
bonate crystals, A rough and ready method, 
said to work well in practice when changing from 
one accelerator to another, is to consider that 
one drop of liquor ammoniz is equivalent in its 
action to 8 gr. of sodium carbonate or 5 grs. 
of potassium carbonate crystals. Dr. Mason 
gives the following comparative table :— 


_ Alkalimeter 19 


Potassium hydrate. ° eenea ges. 
Sodium hydrate . , eka. oy 
Potassium carbonate. St Ob ye 
Sodium carbonate (anhydrous) 106 ,, 
Sodium carbonate (crystals) . 286 ,, 
Sodium bicarbonate ; 2 1168% 4, 

(See also ‘‘ Accelerator.’’) 

ALKALIMETER (Fr. Alcalimétre; Ger., 


A lkalimeter) 

An instrument for testing the amount of 
alkali present in a commercial sample which 
may have an admixture of impurities. It was 
invented by F. A. H. Descroizilles, of Dieppe, 
though some have claimed the discovery for 
Dr. Andrew Ure, of Glasgow. It consists of a 
graduated glass tube divided into 100 degrees 


COUT TTT TTT | 


COO oo rr 


TOOT oo 


HATA 


NON 


ca 


\ 
NN 


\\ 


eam NTT 


Alkalimeter 


B. Burette Pattern 
Alkalimeter 


and furnished at one end with a dropping 


nozzle. The form recommended by Dr. Fara- 
day is shown at A, but many now prefer to use 
the more convenient burette pattern B, hav- 
ing a glass tap or pinchcock at its lower end. 
The tube of the alkalimeter is filled with dilute 
sulphuric acid, containing as much of the strong 
acid as would suffice to neutralise a given weight, 
say 100 grs., of potassium carbonate or sodium 
carbonate. One hundred grains of the alkali 
to be tested is then dissolved in water, the 
solution being placed in a glass beaker or flask, 
and the acid solution is allowed to drop gradu- 
ally into it until the mixture is neutralised. The 
purer the substance the more of the acid will 
be required. If the tube is emptied to, say, 
80 deg., the alkali is known to contain 20 per 
cent. of impurities. The point at which neutral- 
isation occurs used to be determined by means 
of litmus or turmeric, but more sensitive and 
easily recognisable indicators are now employed, 


Alpha Papers 


the principal of these being methyl-orange and 
phenol-phthalein. A mixture of these two re- 
agents in alcoholic solution gives a pale yellow 
colour to a perfectly neutral liquid, which is 
instantly changed to pink by the least trace of 
acid, or to a deep red by a trace of alkali. Com- 
mercial potassium carbonates and sodium car- 
bonates frequently contain a certain proportion 
of the sulphate or chloride, silicates, etc., and 
since the value of the sample depends on the 
proportion of carbonate present it is obviously 
requisite to ascertain this. Impure com- 
mercial alkalis are, of course, scarcely suitable 
for photographic purposes, but the above 
method of testing is often useful. By using an 
alkaline solution of known strength instead of 
the acid solution, the strength of acids may be 
tested ; or the strength of a solution of silver 
may be ascertained by charging the instrument 
with a standard solution of sodium chloride. 


ALKALINE FIXING BATH 

A “hypo” (hyposulphite of soda) fixing 
bath that is not in an acid condition. Fixing 
baths for printing-out papers should always be 
distinctly alkaline, and as ordinary mixtures of 
hyposulphite of soda and water are sometimes 
slightly acid, various methods of destroying the 
acidity have been recommended. A normal 
fixing bath may be rendered alkaline by adding 
sufficient liquor ammonie until after stirring 
it smells faintly, or by adding sodium carbonate 
or bicarbonate. A standard formula for an 
alkaline bath is :— 


Hyposulphite of soda a Odes e124. oe 
Washing soda . ‘ : oe 2 ee 
Common salt . ; tee gee 
Water ; . F 18 1,000 ccs. 


” 


At least one authority considers this too weak, 
and reduces the water to 12 oz. or 140z. Some 
advocate the use of 4 oz. of sodium sulphite 
in place of the + oz. of washing soda. Itis 
not advisable to use this bath with any paper 
having a substratum tinted pink or mauve, as 
these colours, which are aniline dyes, would in 
almost every case be destroyed. 


ALLONGE PAPER 

A rough-grained hand-made drawing paper, 
used by artists in crayon drawing for process 
reproduction. It has a very pleasing surface 
grain, and may be used on the right or wrong 
side with different results, the right side being 
the rougher and perhaps the better. This paper 
may be sensitised for printing a photographic 


image on to it as a guide to the artist. (See 
‘* Sensitising.’’) 
ALLYL-SULPHOUREA, ALLYL-THIO- 


CARBAMIDE, AND ALLYL-THIO- 
UREA (See “‘ Thiosinamine.’’) 


ALPHA PAPERS AND PLATES 

A particular make of chloro-bromide printing 
paper and transparency plate introduced in 1890 
and 1891 respectively by Ilford, Ltd. The plate 
or paper is printed by artificial light, and after- 
wards developed ; the image may then, if desired, 
be toned in a toning bath, which gives a large 
variety of colours. 


Altogravure 


ALTOGRAVURE 

A process for the production of half-tone 
intaglio plates for power-press printing after the 
style of Rembrandt photogravure. 


ALTO-RELIEVO (Fr., Haut 
Hochrelief) 

Derived from the Italian term alto rilievo, 
meaning high relief; applied to sculptured, 
carved, or modelled ornaments and figures which 
stand out from their background by more than 
half their proportionate thickness. The term is 
sometimes employed in processes in which relief 
is obtained by methods depending on the action 
of light, the results so produced being known as 
photo-reliefs. As a rule, however, these pro- 
cesses are not capable of yielding a great amount 
of relief. A low degree of relief is known as a 
basso-relievo, or bas-relief (which see); while a 
medium amount is known as a mezzo-relievo. 


ALUM (Fr., Alun; Ger., Alaun) 

This term comprises a large class of salts 
characterised by the formula M’,SO, M’”’, 
(SO,)3 24H,O, in which M’ and M’” are mona- 
tomic and triatomic metals. All the alums 
crystallise in octahedra, but all do not contain 
alumina. The following are the principal alums 
used in photography :— 


vyelief; Ger., 


Ammonia Alum (Fr., Alun ad’ammoniaque ; 
Ger., Ammoniakalaun) 
(NH,),SO, Al,(SO,); 24H,O. Molecular 
weight, 906. Solubilities, 1 in 8-5 water, inso- 
luble in alcohol and ether. 


Potash Alum (Fr., Alun de potasse ; 
Kalialaun) 

Synonym, aluminium and potassium sulphate. 
K,SO, Al,(SO,); 24H,O. Molecular weight, 
948. Solubilities, 1 in 7:5 water, insoluble in 
alcohol and ether. This is the most generally 
used ‘‘alum,’’ and is met with in large octa- 
hedral clear crystals or a white powder of pecu- 
liar astringent taste. It is used for a hardening 
and clearing bath and for making the “hypo’’ 
and alum bromide toning bath. 

In process work, potash alum is used with dilute 
nitric acid for graining or matting the surface of 
zinc plates previous to coating them with the 
albumen-bichromate sensitising solution. The 
graining makes the coating hold better, and after 
the image has been inked and developed, the 
grained surface holds the damping solution, which 
prevents the ink from spreading and soiling the 
whites when rolling up. 


Soda Alum (Fr., Alun de soude ; Ger., Natri- 

umalaun) 

Synonyms, sodium alum, sodium and alu- 
minium sulphate. Solubilities, 1 in 2-2 water; 
insoluble in alcohol and ether. ‘This is occasion- 
ally used in place of the ammonia or potash alum. 


Chrome Alum (Fr., Alun de chrome; Ger., 
Chromalaun) 

Synonym, chromium and potassium sulphate, 
K,SO, Cr,(SO,), 24H,O. Molecular weight. 
916. Solubilities, 1 in 6:25 water, insoluble in 
alcohol and ether. This is in the form of rich 
violet coloured crystals, giving a dichroic solution 
that is reddish violet by transmitted, and green 
by reflected light, obtained as by-products in 


Ger., 


20 


Alum Baths 


the manufacture of alizarine, aniline violet, etc. 
Stolze suggested the addition of sufficient 
ammonia to chrome alum solution to give a per- 
manent precipitate after well stirring and then 
filtering. Namias suggested the admixture of 
equal quantities of a 10 per cent. solution of 
ordinary and chrome alums, rendering the mix- 
ture alkaline with ammonia, boiling and filtering. 
Lumiére and Seyewetz have also confirmed the 
statement that alkaline chrome alum exerts a 
greater hardening effect. The maximum hard- 
ening effect is produced by 2 per cent. of the 
total dry gelatine employed. 

Chrome alum is used as an addition to emul- 
sions, and for this purpose it is general to render 
the solution distinctly alkaline with ammonia, 
filter, and then render neutral by the addition 
of glacial acetic or hydrobromic acid. It is also 
used in the fixing bath (which see) and combined 
bath (which see). 

Iumiére and Seyewetz have pointed out that 
100 parts of gelatine are most hardened by 
0:64 parts of alumina, and the following table 
gives the quantities of the aluminium compounds 
which contain this quantity of alumina :— 


Potash alum 6 parts 
Ammonia alum ; + Se aay 
Aluminium sulphate : es 


Aluminium chloride, anhydrous 1-6 
Aluminium nitrate. eae 5 


Below these quantities the full hardening effect 
is not produced, whilst increase produces no 
greater hardness. They have also pointed out 
that ‘“‘alum’’ has the least hardening effect, 
and is extremely liable to fungoid growths, 
so that it is far better to use chrome alum in 
its place. 

In process work, chrome alum is used as a 
hardening agent for gelatine. It is added some- 
times to fish-glue when the image has a tendency 
to wash away too freely. Also it has been added 
to the nitric acid bath when etching enamel 
images on zinc, with the object of preventing 
the images from being softened. 


Ivon Alum (Fr., Alun de fer ; Ger., Ammo- 

niaketsenalaun) 

Synonyms, ammonia-iron-alum, ammonio- 
ferric-sulphate, ferric ammonium sulphate. 
(NH,),S5O, Fe,(SO,), 24H,O. Molecular weight, 
962. Solubilities, 1 in 2 water, insoluble in 
alcohol and ether. This is in the form of large 
pale violet or amethyst octahedral crystals, which 
give a brown solution when dissolved in tap 
water, due to the formation of basic iron salts. 
Used for making ferric oxalate (which see). 


ALUM BATHS 

These are used in both negative and print 
making. In negative work an alum bath was 
otiginally used for the purpose of hardening the 
film, but with most modern plates and modern 
improvements in working such treatment is 
rarely necessary. It serves another purpose, 
however. If the bath is rendered acid, alum re- 
moves all development stain and improves the 
colour of the negative. A good formula is :— 


Common alum . : I OZ. 58 g. 
Hydrochloric acid N I drm. 50 ccs. 
Water . « '20°O25 FROG te 


Alum Trough 


After a short rinsing from the developer, the 
plate should be immersed in this bath for two 
or three minutes, then well washed for ten or 
fifteen minutes, and fixed as usual. The use 
of a good acid fixing bath renders the employ- 
ment of an acidified alum bath unnecessary, as 
it clears and hardens the film while fixing is pro- 
gressing, 

In the carbon and allied processes, in which 
a bichromate is used for sensitising, an alum bath 
is employed after the print is developed. Its 
object is twofold. It hardens those parts of the 
film that may remain partially soluble, and also 
removes any yellow bichromate stain that may 
be left after development. The following is an 
excellent formula :— 


Alum 
Water < 


Hot water should be used for dissolving the 
alum, but the bath must not be used until it is 
quite cold. 


ALUM TROUGH 

A glass-sided trough containing alum solution, 
and sometimes used in the optical lantern 
between the light and the condenser in order to 
absorb the heat rays before they reach the slide 
or other object to be projected. Alum troughs 
are widely used for cinematograph films, and 
slides by the screen-plate (colour) processes, as 
these are easily damaged by heat. Glycerine and 
other solutions have been advocated in place of 
a saturated solution of alum, while even plain 
water, circulating through pipes and a tank on 
the thermo-syphon principle, is sometimes 
employed. 


ALUM-HYPO TONING 

A method of toning black-and-white prints 
on bromide and gaslight papers to a sepia colour, 
sometimes referred to as the “‘ boiling process ”’ 
and as “sulphur toning’’; actually it is a sulphur 


T0Z. 
20 


55 &. 
1,000 ccs. 


toning process, but not the only one. The 
formula for the bath is :— 
Sodium hyposulphite 24 0z. 125g. 
Powdered alum See a se 
Granulated sugar + ,, 25°,. 
Boiling water to e2ONe |; 1,000 ccs. 


Dissolve the “‘ hypo ”’ in the water first, add the 
alum slowly, and next the sugar, although this 
may be omitted if desired. When all is dissolved 
the solution should be milk white and a sediment 
should form at the bottom of the bottle, but it 
should not be filtered. The bath should be 
heated two or three times to about 120° F. 
(nearly 49° C.), allowing to cool in between ; 
this “ripening” is necessary»because were it 
omitted the newly-made bath would not work 
well, and would bleach the prints. The older 
and more used the bath is (it may be used over 
and over again) the more evenly it works, and 
the richer the tones. When possible, one part of 
an old bath should be added to four parts of the 
new bath. Another method of ripening the bath 
is to tear up some old prints and place in the 
solution previous to heating; still another is to 
add 5 grs. of silver nitrate to each ounce of the 
bath, this tending to give a purplish-brown tone. 
The fixed black-and-white prints to be toned 


21 


Aluminium 


should be placed in the bath when this is cold, 
and the whole then warmed, keeping the prints 
on the move. The time of toning will vary 
according to the kind ot paper and developer, 
age of print, and temperature of solution. The 
quickest results are obtained by raising the 
temperature as high as the picture will stand, 
generally about 100° F. (nearly 38° C.), but the 
best tones are those obtained at about 85° F. 
(between 29° and 30° C.), the average time being 
fifteen minutes. The bath may be used cold, 
in which case toning may take as long as two 
or three days. Prints developed with amidol 
appear to tone the quickest, and those toned 
with hydroquinone the slowest. When the 
prints reach the desired tone they are allowed to 
remain in the solution until it is tepid, or cold, 
and then well washed. 

Another method of toning with this bath is 
to harden the prints first of all in a solution of 
alum (alum 1 oz.; water 30 0z.), or a portion of 
the cold toning bath, and then place in the alum- 
hypo bath made hot, and, after toning, in the 
alum-and-water solution again, finally washing. 
The object of the alum baths is to prevent 
blisters, which would in all probability occur if 
the prints were put direct into the hot toning 
bath, and thence into cold water for washing. 
The use of the extra alum baths is obviated by 
warming the toner containing the prints. Rich 
and good tones depend upon the print having 
been properly developed, and upon the ripeness 
of the bath. If the toned prints are washed for 
about one hour they may be considered quite 
permanent, the image consisting of silver sul- 
phide. 

The alum-hypo bath may also be used for 
toning P.O.P. prints. The prints must first be 
washed, fixed in an ordinary “‘hypo” bath, next 
placed in a cold alum-hypo bath, where they tone 
to a good purple-brown colour, and then washed 
well. P.O.P. prints to undergo this treatment 
should be over-printed, since they reduce con- 
siderably in toning. 


ALUMINIUM, OR ALUMINUM (Fr. 
Ger., Aluminium) 

Al. Atomic weight, 27. A very light, sil- 
very-white metal, obtained by electrolysis from 
aluminium chloride. It is principally used for 
the construction of light cameras and for lens 
fittings, but difficulties in working it and its soft- 
ness led to the introduction of a harder alloy 
of aluminium and magnesium, called magnalium. 
Aluminium is used in some flashlight powders, 
and in algraphy (which see). ‘“‘ Aluminum’? is 
now the accepted American spelling. 

Aluminium plates are now largely used for 
lithography as a substitute for lithographic © 
stone. (See “ Algraphy.’’) 

In process work, aluminium has been used for 
relief etching, but is not commercially in vogue. 
Nitric acid has little action on it, but hydro- 
chloric acid attacks it more readily. Phos- 
phoric and fluo-silicic acids are active mordants, 
but not convenient to use. Perchloride of iron 
has a strong action upon it ; a solution of common 
salt will also attack it freely. Aluminium is 
largely used for the screen and plate holders of 
process cameras, as it is mot readily acted on 
by the silver nitrate solution. 


and 


Aluminium Chloride 


ALUMINIUM CHLORIDE (Fr., Chlorure 
dalumine ; Ger., Chlovaluminium) 

Al,Cl, 12 H,O. Atomic weight, 483. Soluble 
in water, alcohol, and ether. It is a yellowish- 
white granular crystalline powder which (very 
rarely) is used in the gold and platinum toning 
baths. It is extremely deliquescent, and must 
be kept in well-stoppered bottles. 


ALUMINIUM FLASHLIGHT 

Aluminium bronze powder, also known as 
“‘ silver bronze,’’ may be used in place of, or in 
conjunction with, magnesium for flashlight work. 
It is cheaper than magnesium, burns under cer- 
tain conditions with less smoke, but it is not 
quite so actinic. The first experiments with 
this metal appear to have been carried out by 
Dr. Piffard, of New York, in 1888. Dr. Miethe 
has found that fine aluminium bronze powder 
(5 to 10 per cent. of aluminium and 90 to 95 
per cent. of copper) burns almost completely in 
the flame of a Bunsen burner. Aluminium, how- 
ever, is better, even if more dangerous, when 
mixed with potassium chlorate, in which form it 
becomes an explosive mixture, and must be 
treated as such; that is to say, the mixture 
must have a light applied to it, and not be blown 
through a flame. The potassium chlorate 
intended for mixing with the aluminium bronze 
powder should be quite free from the deliques- 
cent potassium chloride, because if this is present 
the chlorate will tend to be moist. The chlorate 
should be well dried, and powdered sufficiently 
finely as to pass through a sieve of eighty meshes 
to the inch. The aluminium and the chlorate 
must not be mixed together in a mortar, but 
with a feather or a flat blade on a sheet of paper. 
A suitable formula is :— 


Aluminium ; 5 c I 
Potassium chlorate 


part. 
24 parts. 


For more rapid flashes, antimony sulphide should 
be added, the formula being :— 


Antimony sulphide . eo SQ DaEGd 

Aluminium . . p 5 99 

Potassium chlorate . paenk S Hf 
Another formula is :— 

Aluminium : . - 20 parts. 

Lycopodium . . » 

Ammonia nitrate I part. 


All these mixtures are explosive and dangerous, 
and proper precautions should be observed, 
as directed under the heading ‘* Flashlight 


Mixtures,” where a formula for aluminium 
in conjunction with magnesium will be 
found. 


A flashlight mixture, patented in 1904 by Dr. 
G. Krebs, gives very little smoke and consists 
of aluminium 2 parts, magnesium 2 parts, and 
chrome alum 10 parts. A “time” powder, also 
due to Dr. Krebs, contains aluminium 20 parts, 
magnesium 80 parts, chrome alum or copper 
sulphate 100 parts, lime oxide, carbonate, or 
glass 20 parts. Aluminium cartridges, to con- 
tain a flash mixture and burn with it, have 
lately been made, the metal case being of from 
"r to *3 mm. thickness. 

Aluminiun leaf burned in oxygen gives a very 


22 


Amber 


powerful light. The method is to place a few 
leaves of aluminium in a dry bottle containing 
oxygen gas, and on applying a lighted taper to 
the top leaf the contents of the bottle burn with 
a flash which, for actinic power and general 
brightness, is said to exceed anything obtainable 
with an equal amount of magnesium. 


ALUMINIUM POTASSIUM SULPHATE 
(See ** Alum.,’’) 


ALUMINIUM SULPHATE (Fr., Sulfate @ alu- 
mine ; Ger., Aluminiumsulfat) 

Al,(SO,), 18 H,O. Molecular weight, 166. 
Solubility, 1 in 2 water. White crystals with 
sweet, astringent taste, obtained by dissolving 
aluminum hydrate in sulphuric acid. It has 
been suggested as a hardening agent, but has 
found very little use. 


ALUMINIUM SULPHOCYANIDE (Fr., Su/fo- 


cyanure dalumine; Ger., Aluminium- 
rhodantd) 
Synonym, aluminium sulphocyanate or 
rhodanide. Al,(CNS),. Molecular weight, 402. 


A yellowish powder occasionally used as a 
preliminary bath for self-toning papers. It is 
extremely deliquescent, and must be kept in well- 
stoppered bottles. 


ALUMINOGRAPHY (See “ Algraphy.’’) 


AMACRATIC 


A term relating to photographic lenses and 
implying that the chemical rays of light are 
united into one focus. ‘“‘ Amasthenic’”’ is a term 
with the same meaning. 


AMASTHENIC 


AMATEUR PHOTOGRAPHER 

One who practises photography as a pastime, 
and not as a profession. In photography the 
question of who is and who is not an amateur is 
a difficult one to decide. So-called amateurs do 
not hesitate to accept a little payment for their 
prints “‘just to cover the cost of materials,’ 
while others win prizes in cash competitions, or 
sell prints to periodicals. It is maintained in 
many quarters that the acceptance of money 
by an amateur for his work places him in the 
professional category. The consensus of opinion, 
however, is that a photographer who does not 
advertise, invite custom, or rely upon the art as 
a livelihood, is an amateur. The old controversy 
and jealousy between amateurs and professionals 
has, at any rate in Great Britain, faded away 
to extinction, and the two classes of photo- 
graphers understand more clearly that their 
interests are parallel and do not clash, and 
that photographic progress has need of them 
both. 


AMBER (Fr., Ambre jaune; Ger., Bernstein) 

A fossil, yellow and translucent resin used 
occasionally in varnishes, for which purposes it 
must first be fused. 


Fused amber 3 02. 150 g. 
Chloroform to . », 20.9) 2, CoGhers. 


When dissolved, filter and use cold. 


(See ‘* Amacratic.’’) 


_—- 4 
—_—, ae = 


Ambrotypes 


Another formula is that known as Brannt’s, 
namely :— 


Fused amber - 4 OZ 400 g 

Sandarac 6”; 600 ,, 

Elemi . : : ‘aes hie 100 ,, 

Methylated spirit (90%) . 12 ,, 1,000 ccs 
When dissolved add— 

Camphor 4 02. 12} g. 
AMBROTYPES 


The American name for wet collodion positives 
upon glass or “tin” (thin plates of enamelled 
iron or steel), Those upon glass are some- 
times said to be by the “ alabastrine process ”’ 
(which see); those upon “tin” are called ‘“‘ tin- 
types” or “ferrotypes.’’ Ambrotypes are pro- 
duced by the “ finished while you wait ”’ process 
formerly so extensively practised by itinerant 
photographers, but now practically superseded. 
Full particulars will be found under the heading 
*““Ferrotype Process.” 


AMIDINE (Ftr., Amidon ; Ger., Amidin) 

Synonyms, amadine, amylum. An amyl- 
aceous substance identical in chemical composi- 
tion with cellulose, and found in many cereals 
and vegetables. It is practically equivalent to 
starch. It forms the translucent jelly or paste 
obtained when boiling water is poured on ordinary 
starch, so extensively used as a photographic 
mountant. 


AMIDO-ACETIC ACID (Fr., Glycocoll; Ger., 
Amidoessigséure, Glykokoll) 

Synonyms, glycocoll, amido-glycollic acid, 
amino-acetic acid, glycocine, sugar of gelatine. 
NH, CH, COOH. Molecular weight, 75. Solu- 
ble in water. White crystals, formed by re- 
placing one of the hydrogen atoms of ammonia 
by the acetic acid. It possesses both acid and 
basic properties, and the sodium salt NH, CH, 
COONa was introduced (1902) under the name 
of Pinakolsalz N by Meister, Lucius and Briin- 
ing as a substitute for the alkalis in developers, 
but on account of its high price did not replace 
them in practice. 

Amido-acetic acid is called sugar of gelatine 
on account of its sweet taste, and from its being 
a product of the decomposition of gelatine by 
acids or alkalis. It is sometimes termed glycin, 
but must not be confused with the developer of 
that name (which see), this being a phenol de- 
rivative of it, having the formula C,H,OH NH 
(CH,COOH). 


AMIDO-BENZINE (See “ Aniline.’’) 

AMIDO-CARBOXYLIC ACIDS (See ‘ Carb- 
oxylic Acids.’’) 

AMIDO-GLYCOLLIC ACID (See ‘ Amido- 
acetic Acid.’’) 

AMIDO-PHENOL (See ‘‘ Amidol.’’) 


AMIDOL, OR DIAMIDOPHENOL (Fr. and 
Ger., Amidol) 

A developer having the formula C,H, 

OH(NH,), ,and introduced in the year 1892. It 

is sold in the form of a white or greyish crystal- 


23 


Amidol 


line powder, which keeps well in a dry state but 
in solution rapidly loses its developing powers. 
The dry amidol is therefore best added to the 
solution immediately before use. It forms a 
developer when mixed with a solution of sodium 
sulphite, no alkali being needed, and it works 
very rapidly, the detail appearing almost imme- 
diately the developer is applied to the plate. 
This sudden appearance is apt to deceive those 
unacquainted with it, but the negative must not 
be taken from the developer until it has attained 
the required density. It has been stated that 
amidol will develop when in an acid condition, 
and appropriate formule have been published, 
but it is better to regard amidol as an alkaline 
developer, because, even if it does work when 
slightly acid, it works better when slightly 
alkaline. The addition of acetone sulphite in 
quantity equal to that of the amidol preserves 
the developer for a considerable time, but acts 
as a restrainer; other preservatives have been 
advocated, but it is better to add the dry amidol 
when required for use. A normal developer 
consists of :— 


Sodium sulphite 600 gts. 60 g. 
Amidol e 4060 oF ge 
Water to 20 OZ. 1,000 ccs. 


The mixed developer will keep well for four or 
five days. It should be made up with a new 
solution of fresh and pure sulphite. It is usual 
to make up a stock solution of sodium sulphite 
and to add 2 to 3 grs. of dry amidol to each 
ounce of solution. 

Potassium bromide has but little restraining 
effect in an amidol developer, except when used 
in large quantities, but when added in small: 
quantities it has a clearing effect. In cases of 
over-exposure, about 15 drops of a Io per cent. 
solution of potassium bromide may be added 
for every ounce of developing solution. Acetic, 
citric, and tartaric acids have been recommended 
as restrainers and sodium hyposulphite (“‘ hypo ”’) 
as an accelerator, but with the latter the image 
loses density beyond a certain point. Two- and 
three-solution amidol developers are rarely 
tesorted to, as they have but little advantage 
over the one-solution, which is in wide use, par- 
ticularly for bromide paper, for which most 
paper-makers give a special formula. ‘The two- 
solution form is not given here because it is of 
doubtful value. 

Amidol has the property of staining the 
finger-nails. Sometimes it stains bromide prints 
a rosy pink colour, which may be removed by 
the use of eau-de-javelle followed by citric acid. 

Another formula with bromide, and specially 
recommended by Abney for the development of 
“instantaneously ’’ exposed plates, is :— 


Amidol : gt are 5 g. 
Sodium sulphite : = 40? 3, Fo a 
Potass. bromide ay | I 


»? 


Water to 2 OZ, 1,000 ccs. 


This solution will keep for a few days, but is 
most energetic when fresh. 

Another form of a one-solution amidol de- 
veloper is that known as Balagny’s acid-amidol, 
which has found great favour upon the 
Continent, both for negatives and bromide 


paper. 


Ammonia 

One of its advantages is its slowness, The 
original formula is :— 

Water . 10% OZ. 300 ccs. 
Amidol ; : 30. «agrs. 2.8. 
Sodium sulphite 

crystals ag LOO ar. 3... 
Potassium bromide 

solution (10 %) . 170 mins. 10 ccs. 
Sodium  bisulphite 

solution FER TOY © (3 oe aoe 


The bisulphite solution is a commercial article. 
A substitute can be made by preparing a satu- 
rated solution of the commercial bisulphite and 
then adding 1 drm. of strong sulphuric acid to 
each 4 pint. Many similar acid-amidol mixtures 
have been advocated. 

It has been frequently stated that amidol- 
developed negatives and prints should not be 
fixed in an acid fixing bath, because of its 
causing fogging or further development during 
fixation, but T. H. Greenhall says that there is 
nothing to be feared in this respect when using 
bromide paper. An old acid fixing bath heavily 
charged with amidol and sulphite gave stronger 
prints than plain “hypo,” due to the fact 
that plain “hypo” had a slight reducing 
action, and not to any defect in the acid 
fixer, which was absolutely necessary for some 
papers. 

Some photographers find that amidol has an 
effect upon the skin resembling that of metol, 
but not so intense. 


AMMONIA  (Fr., Ammontaque ; Ger., Ammo. 
niak, Ammoniakwasser, Salmiakgeist) 

A volatile, Me dat gas, which for photographic 
and many other purposes is used in the form of 
a watery solution (NH;0H); formerly known 
as “‘spirit of hartshorn.” The strongest solu- 
tion, and that mostly used, is of -880 sp. g., 
contains 35 per cent. of the gas NH, and is 
commonly known as ‘“‘ ammonia *880” or “liq. 
ammon. fort.” ‘“‘Liquid ammonia” is the 
incorrect, popular form of the term “ liquor 
ammonie,.”” A weaker liquor, kept by most 
chemists, one-third the strength of the -880 
solution, is rarely used in photography. Ammo- 
nia has many uses in photography, the principal 
being as an accelerator in the pyro developer, 
for blackening the mercury-bleached image in 
intensification, in emulsion-making, and as an 
addition to the bichromate bath for sensitising 
carbon tissue. Liquor ammonie should be kept 
in a _ glass-stoppered bottle, as it loses its 
strength rapidly if exposed to the air, and cork 
stoppers very soon deteriorate. The fumes of 
ammonia are extremely irritating to the eyes, 
throat, and nose, and particular care should be 
taken when opening bottles of it in hot weather, 
or when the bottles have been left on a warm shelf, 
as the liquid may spurt out and cause serious 
damage. Bottles containing liquor ammoniz 
should be kept in a cool place, as heat develops 
great pressure, which may blow out the stopper 
or burst the bottle. 

A. Haddon states that experiments show 
that ammonia expands on dilution with water 
about 18 per cent., and points out how very un- 
reliable and varying is a solution of ammonia 
in hot weather, freshly bought samples of the 


24 


Ammonium Bichromate 


*380 solution varying in specific gravity from 
that to -904, or from 35-8 to 26-9 NH; per cent. 
volume. It is this variation that makes it 
unreliable as an accelerator in development ; 
hence the necessity of using it fresh or keeping it 
in a gas-tight bottle and in the cool. 

In process work, ammonia is not largely used. 
It is added to the albumen bichromate solution 
and also to the fish-glue solution to neutralise 
acidity, and increase the keeping qualities. A 
few drops added to the developing water makes 
the albumen bichromate image develop more 
quickly. A dilute solution of ammonia with 
whiting is used for cleaning copper, to free the 
surface from grease. Perchloride of iron solution 
for etching, especially for photogravure, is often 
neutralised by the addition of ammonia. Added 
to copper sulphate until a bright blue solution is 
formed, ammonia makes a bath for coating zine 
with a film of copper without the use of an elec- 
tric battery. 


AMMONIA FUMING 

Years ago, when most photographers, both 
professional and amateur, prepared their own 
plain salted and albumenised papers, it was 
customary to expose these to the fumes of 
ammonia in a box. The ammonia, uniting with 
the free silver nitrate in the paper, gave greater 
sensitiveness and richer prints. It has now 
fallen into almost entire disuse, but it formerly 
found favour owing to the brilliance imparted 
to the prints so treated. 


AMMONIA METER 

A small glass bulb, devised by Haddon and 
Grundy, which floated at exact balance in a 2°9 
per cent. solution of ammonia of a certain 
temperature, thus enabling the strength to be 
determined without analysis. It has also been 
known as a “ specific gravity ball.” 


AMMONIA-IRON-ALUM (See “ Alum.’’) 

AMMONIA, ROCK (See “ Ammonium Car- 
bonate.’’) ' 

AMMONIO.-CITRATE OF IRON (See 
‘* Ferric Ammonio-citrate.”’) 

AMMONIO-NITRATE PROCESS (See 
** Emulsion.’’) 

AMMONIO-OXALATE OF IRON (See 
“Ferric Ammonio-oxalate.’’) 

AMMONIUM $ (See ‘‘ Ammonia,’’) 


AMMONIUM ALUMINIUM SULPHATE 
(See “ Alum.’”) 


AMMONIUM BICHROMATE (Fr., Bichro- 
mate d’ammoniaque ; Ger., Ammonium- 
dichromat; Saures chromsaures ammon) 

(NH,),Cr,O,. Molecular weight, 252. Solu- 
bilities, 1 in 4 water, soluble in alcohol; known 
also as ammonium dichromate. Orange crystals, 
obtained by neutralising chromic acid with 
ammonia. It is sometimes used for sensitising 
carbon tissue, gum bichromate, and in some 
photo-mechanical processes, as it has a stronger 


Ammonium Bromide 


sensitising power, and is more soluble than the 
potassium salt, and in carbon printing gives 
richer pictures. 

In process work, ammonium bichromate is 
largely used as a sensitiser with fish-glue for 
printing half-tone images on zinc and copper. 
It is believed to be a better sensitiser than 
potassium bichromate in this respect, the latter 
being chiefly used with albumen for the line 
process. It gives a more sensitive solution with 
fish-glue, the solution keeps better, and develops 
more freely. Ammonium bichromate is said to 
be more than twice as sensitive to light as 
potassium bichromate. 


AMMONIUM BROMIDE (Fr., Bromure 
dammonium ; Ger., Bromammonium) 

NH,Br. Molecular weight, 98. Solubilities, 
I in 1-4 water, I in 31 absolute alcohol. A white, 
crystalline, slightly hygroscopic powder, with 
pungent saline taste, obtained by neutralising 
hydrobromic acid with ammonia, evaporating 
the solution and crystallising. It is sometimes 
used as a restrainer in place of the potassium 
salt, but must not be used with the caustic 
alkalis or carbonates, as ammonia is set free, 
which may give rise to fog. Its principal use 
is in emulsion making. If the salt has become 
damp by absorption of aqueous vapour, it may 
be dried in an oven without injury. 


AMMONIUM CARBONATE (Fr.,  Car- 
bonate d’ammontaque; Ger., Kohlensaures 
ammon, Ammoniumkarbonat) 

Synonyms, hartshorn, rock ammonia. 
(NH,)HCO, (NH,)NH, CO,. Molecular weight, 
157. Solubility, 1 in 4 water. Keep in well- 
stoppered bottle, and before use scrape off any 
adherent white powder. White, hard, translu- 
cent, striated masses, obtained by heating 
ammonia salts and chalk. It is used in place of 


liquor ammoniz in some developers. Hot water 
must not be used to dissolve it. 
AMMONIUM CHLORIDE (Fr., Chlorure 


dammontaque ; Ger., Chlorammonium) 

Synonyms, sal-ammoniac, muriate or hydro- 
chlorate of ammonia. NH,Cl. Molecular weight, 
53°5. Solubilities, 1 in 3 water, 1 in 8 alcohol. A 
white, crystalline powder, or tough, transparent, 
fibrous masses, the latter usually known as sal- 
ammoniac. The pure powdered salt is apt to 
attract aqueous vapour from the air, whilst sal- 
ammoniac remains dry. It is chiefly used for 
salting albumenised paper and also in preparing 
chloride emulsions. 


AMMONIUM’ CITRATE  (Fr., Citrate 
dammoniaque ; Ger., Ammoniumcitrat) 
(NH,);C,H,O,. Molecular weight, 243. Solu- 
bility, 1 in 0-5 water, soluble in alcohol. This 
salt is so deliquescent and so easy to make that 
the user should prepare it himself :— 
Citric acid Te Or; I0O g. 
Distilled water 2 200 ccs. 


When dissolved add— 
Liq.ammonie -880, (about) 250 mins. 


»? 


50 ccs. 


The ammonia should be cautiously added, and 
the solution tested for neutrality with litmus 


& 


Ammonium Molybdate 


paper. When neutral, make the total bulk up 
to 10 oz. or 1,000 ccs. with distilled water, 
which practically gives a 10 per cent. solution. 
It is used as a restrainer with the pyro developer 
in the proportion 5 to Io grs. per ounce. 


AMMONIUM FLUORIDE (Fr., Fluorure 


dammonium; Ger., Fluorammon) 


NH,F. Molecular weight, 36. Soluble in water 
and alcohol. This isin the form of small, deliques- 
cent, colourless, flat crystals, and it is used for 
etching glass and stripping negatives. As it 
attacks glass, it must be kept in indiarubber or 
wax-lined bottles. 


AMMONIUM HYDRATE 


A very seldom used synonym for liquor 
ammonie, NH,HO. 
AMMONIUM HY DROSULPHIDE (See 


“Ammonium Sulphydrate.”’) 


AMMONIUM HYPOSULPHITE (Fr., Hypo- 
sulphite @ammoniaque ; Ger., Ammonthio- 
sulfat) 

Synonym, ammonium thiosulphate. (NH,), 
S,0O,;. Molecular weight, 148. Very soluble in 
water. It occurs in colourless crystals, or can 
be readily made in solution, as follows :— 


Sodium hyposulphite . 5 oz. 248 g. 
Ammonium chloride . 24 ,, TOO 
Distilled water to 20° 5, 1,000 ccs. 


It was suggested first in 1888 by John Spiller 
as a substitute for the sodium salt, on account 
of its greater solubility, and therefore of the 
greater ease with which it can be washed out of 
prints and negatives. It has recently been 
patented as a fixing salt. Lumiére and Seyewetz 
point out that fixation is only quicker when the 
proportion of thiosulphate is less than 4o per 
cent., and if the proportion of chloride is only 
sufficient to convert one-fourth of the sodium 
salt, and further that the use of this salt must be 
regarded with suspicion on account of the rapid 
decomposition of the silver salts formed if the 
subsequent washing is not very rapid. 


AMMONIUM IODIDE (Fr., lodure dammo- 
nium; Ger., Iodammon) 

NH,I. Molecular weight, 145. Solubilities, 
I in 0-6 water, 1 in 9 alcohol, slightly soluble in 
ether. It is a white to yellowish-white hygro- 
scopic crystalline powder, which is very unstable, 
readily giving off iodine, which may be dissolved 
out by ether. It is occasionally used in 
making iodised collodion and negative gelatine 
emulsions. 

In process work, ammonium iodide is a con- 
stituent in most iodising formule. 


AMMONIUM MOLYBDATE (Fr., Molybdate 
d’ammoniaque; Ger., Molybddénsaures 
ammonium) 

(NH,);Mo,0.44H,O. Molecular weight, 1,236. 
Soluble in water. It is in the form of large 
colourless or slightly greenish crystals, readily 
decomposed by heat. It has been suggested as 
an ingredient in printing out emulsions in order 
to obtain greater contrast. 


Ammonium Nitrate 


AMMONIUM NITRATE (Fr.,  <Azotate 
@ammonium ; Ger., Salpetersaures ammon) 
NH,NO,. Molecular weight, 80. Solubilities, 
I in o*5 water, 1 in 2:25 alcohol. ‘These colour- 
less, long, rhombic crystals are obtained by 
neutralising ammonia or ammonium carbonate 
with nitric acid. It has been suggested as a 
substitute for the potassium salt in flashlight 
mixtures (which see), though its hygroscopic 
nature is somewhat against it. It is also formed 
in emulsion making by double decomposition 
between ammonium bromide and silver nitrate, 
and is removed in washing. It is deliquescent, 
and should be kept in well-stoppered bottles. 


AMMONIUM OXALATE  (Fr., Oxalate 
d’ammontaque ; Ger., Ammonoxalat) 
(NH,),C,0,H,O. Molecular weight, 142. 
Solubilities, 1 in 25 water. It is in the form of 
colourless crystals, obtained by neutralising 
oxalic acid with ammonia, and it is used to pre- 
pare ferric ammonio-oxalate. 


AMMONIUM PERSULPHATE (Fr., Per- 
sulfate d’ammoniaque; Ger., Ueberschwe- 
felsauves ammonium) 

(NH,), S,0,. Molecular weight, 228. Solu- 
bility, 1 in 2:5 water. It takes the form of 
colourless crystals, which are obtained by electro- 
lysis. It is principally used as a reducer, and is 
especially valuable in that it reduces the high 
lights more than the shadows. The following 
formula may be used :— 


Ammonium persulphate 480 grs. 50 g. 
Distilled water to 20 0Z. 1,000 ccs. 


The negative should be immersed in this until the 
reduction is nearly complete, and then rapidly 
washed. A stop bath of sodium sulphite (5 per 
cent. solution) is sometimes recommended, but it 
occasionally gives rise to stains, and it is better 
to use water only. The chemical action which 
takes place is supposed to be— 


Ag +(NH,), S,O, = (NH,), SO, + Ag,SO, 


Silver Persulphate Ammonium Silver 
sulphate sulphate 
The silver sulphate dissolves in water. Namias 


states that a solution of persulphate acidified 
with nitric acid acts like the ordinary “hypo” 
and ferricyanide reducer. 

The addition of 0-5 to 1 per cent. to the normal 
platinotype developer shortens the scale of 
gradation, and is thus useful for over-exposed 
prints. 

H. W. Bennett has made a special study of 
ammonium persulphate as a reducer, and his 
special formula will be found under the heading, 
*“* Bennett’s Reducer.” The addition of ammo- 
nium sulphocyanide has been recommended, this 
causing the persulphate reducer to act in the 
opposite way—namely, to clear the shadows 
first after the manner of the ferricyanide and 
“hypo” reducer, which makes it particularly 
suitable for negatives of line subjects. The 
formula for the persulphate reducer often re- 
ferred to as ‘‘ Puddy’s reducer” is: water I oz., 
ammonium persulphate 25 grs., and ammonium 
sulphocyanide (10 per cent. solution) 120 minims. 
Namias advocates a 5 per cent. solution of per- 
sulphate made acid with 1 per cent. of sul- 
phuric acid for developing over-exposed carbon 


26 


Ammonium Sulphocyanide 


prints. Ammonium persulphate has also been 
suggested as a “hypo” eliminator, stain 
remover, and as an addition to the oxalate 
developer for platinotypes ; $ to 1 per cent. added 
to the normal oxalate developer shortens the scale 
of gradation and saves over-exposed prints. 


AMMONIUM PHOSPHATE (Fr., Phosphate 
@ammonium ; Ger., Ammonphosphat, 
Phosphorsdéures ammontiak) 

Synonyms, hydrogen diammonium phosphate, 
diammonium orthophosphate, dibasic phosphate 
of ammonia. (NH,),HPO,. Molecular weight, 
132. Solubility, 1 in 4 water. Sometimes used 
in emulsion making and in toning, but infre- 
quently ; its chief use is in fireproofing fabrics. 
It is obtained on drying the normal, or neutral 
ammonium phosphate (NH,)sPO,. The latter 
is made by mixing phosphoric acid and ammonia 
in concentrated solution; on cooling, the normal 
salt crystallises out in short prismatic needles. 


AMMONIUM AND POTASSIUM CHRO- 
MATE (Fyr., Chromate d@’ammonium et 
potasse; Ger., Kaliammonitumchromat) 

NH,KCrO,H,O. Molecular weight, 191. Solu- 
ble in water. The pure salt occurs in bright, 
yellow crystals, but is rarely used except in the 
form of a solution which is made by adding 
ammonia to potassium bichromate solution. It 
has been suggested as an improved sensitiser 
for carbon printing, etc., but it frequently makes 
the tissue horny and reticulated. 

In process work, when making up this bichro- 
mate sensitising solution for carbon printing, 
collotype, photo-lithography, and zinc printing, 
it is usual to add liquor ammonize drop by drop 
until the solution turns a light lemon yellow, 
and distinctly smells of ammonia. This forms 
the double chromate of potassium and ammo- 
nium. 


AMMONIUM SULPHIDE (Fr., Suifure 
@ammonium ; Ger., Schwefel-ammonium) 

A yellowish solution, formula (NH,),S, having 

a most objectionable smell; known also as sul- 
phuret of ammonia. It is widely used for toning 
bromides to a brown colour after bleaching, also 
for toning P.O.P. Its evil odour and bad-keeping 
qualities are reasons why some prefer to make 
it as required, according to the following method : 
A. Sodium sulphide, 4 0oz.; water, 24 oz. B. 
Ammonium sulphate, 24 grs.; water, 23 oz. Mix 
A and B, and use at once or any time within 
ten or twelve weeks; in this form its odour is 
not so bad. Ammonium sulphide should not 
be kept in the same room as sensitive plates and 
papers, as the vapour acts injuriously upon them. 
In process work, ammonium sulphide has been 
extensively used for blackening wet plate nega- 
uves after lead or copper intensification, but is 
now being largely superseded by sodium sulphide, 


AMMONIUM SULPHOCYANIDE (Fr., Suifo- 


cyanure dammonium; Ger., Rhodan- 
ammonium) 
Synonyms, sulphocyanate, thiocyanate, or 


rhodanide of ammonia. NH,CNS. Molecular 
weight, 76. Solubilities, 1 in 0-6 water, very 
soluble in alcohol. It is very hygroscopic, and 
should be kept well stoppered. It takes the 


Ammonium Sulphydrate 


form of colourless crystals, obtained from carbon 
disulphide, strong alcohol, and liquor ammoniz, 
It is used in toning printing-out papers. (See 
“Potassium Sulphocyanide.’’) 

A 5 per cent. solution of the sulphocyanide 
will dissolve gelatine in the cold, and it has 
therefore been used to develop over-exposed 
carbon prints. 

Owing to the highly deliquescent properties 
of this salt, it is a common practice to make it 
up into a nominal 1o per cent. solution as soon 
as possible after buying. 1 oz. of the salt should 
be dissolved in 2 oz. or 3 oz. of water, and then 
made up to a total bulk of 9 oz. Ten drops of 
this stock solution will then contain 1 gr, so 
that any toning formula may be made up from 
it with less trouble than by weighing the damp 
solid. Two drms. (120 drops) contain 12 grs., 
which is a good average quantity to mix with 
I gr. of gold chloride and 8 oz. of water. 


AMMONIUM SULPHYDRATE (Fr., Sulphy- 
dvate dammontaque; Ger., Schwefelam- 
mon) 

Synonyms, ammonium hydrosulphide, ammo- 
nium sulphide. NH,HS. Molecular weight, 50. 
Soluble in water. The pure salt occurs in 
colourless, crystalline masses, which rapidly turn 
yellow on exposure to the air. The commercial 
ammonium sulphide, which is generally used, is 
prepared by passing sulphuretted hydrogen H,S 
into liquor ammonize NH,OH, and forms (NH,), 
S = 68, a colourless or slightly yellow solution 
with disagreeable odour. It is used for blacken- 
ing wet collodion negatives after intensification 
with silver iodide, copper bromide, or lead nitrate. 


AMMONIUM THIOCYANATE 
monium Sulphocyanide.’’) 


AMMONIUM THIOMOLYBDATE (Fr., Sulfo- 
molybdate d’ammonium ; Ger., Ammoniak 
thiomolybdanat) 

{NH,),.MoS,. Molecular weight, 260. Solu- 
bilities, soluble in water, insoluble in alcohol. It 
takes the form of red scales obtained by boiling 
molybdenum trisulphide in ammonium sulphide. 
Its use has been patented for sulphiding bromid 
prints in place of sodium sulphide. 


(See ** Am- 


AMMONIUM VANADATE (Fr., Vanadate 
dammoniaque ; Ger., Vanadinsaures am- 
montak) 

Synonym, ammonium metavanadate. NH, 
VO,;. Molecular weight, 116. Slightly soluble 
in water. These colourless crystals have been 
recommended as an addition to printing-out 
emulsions to increase contrast. 


AMPHITYPE 

One of the many curious and interesting print- 
ing processes invented by Sir John Herschel, but 
of no practical value. It depends upon the 
light-sensitiveness of ferric, mercuric, and lead 
salts, and it gives a rich, vigorous print which 
can be viewed from both sides of the paper, or 
as a transparency. A sheet of paper is pre- 
pared with a solution, either of ferro-tartrate 
or ferro-citrate of protoxide, or peroxide of 
mercury, and then with a saturated solution of 
ammonia-citrate of iron. Exposed in a camera 


27 


Amyl Acetate 


for a time varying from half an hour to five 
or six hours, according to the intensity of the 
light, a negative is produced on the paper which 
gradually fades in the dark, but may be restored 
as a black positive by immersion in a solution 
of nitrate of mercury, and ironing with a very 
hot flat-iron. 

Amphitype is also the name of a photo-litho- 
graphic transfer process invented by W. H. 
Shawcross, of Liverpool. The paper is sensi- 
tised with an iron salt, and keeps indefinitely. 
It is printed under a negative, then inked all 
over with a special ink, and developed with a 
solution of yellow prussiate of potash. The lines 
of the print are thus covered with transfer ink 
whilst the ground is a deep blue, which, however, 
can be bleached away in a solution of common 
soda. The transfers are applied to zinc or stone 
in the usual way. 


AMPLIFIER 


A supplementary lens placed between a posi- 
tive or image-producing lens and the focusing 
screen for the purpose of producing an enlarged 
image. Amplifiers may be positive or negative 
in their form; if positive, they must be placed 
outside the principal focus of the primary lens, 
as in the Dallmeyer photo-heliograph or as in 
photo-micrography, where the eyepiece (usually 
of special design) forms the amplifier. When 
negative amplifiers are used, they may be placed 
at any point between the back surface of the 
primary lens and the principal focus; the size 
of image and the necessary camera extension 
become greater as the negative lens approaches 
the positive one. The earliest practical form of 
negative amplifier was the Barlow lens, designed 
for shortening the tube length of telescopes. The 
principle is extensively employed in the con- 
struction of the telephoto lens, in which the 
amplifier is usually termed the “negative 
element.” (See “‘ Telephoto Lens ”’ and “* Photo- 
heliograph.’’) 


AMSTUTZ PROCESS (See “ Acrograph.’’) 


AMYL ACETATE (Fr., Acéiated’amyle; Ger., 
Amylacetat, Birnendl) 

Synonyms, essence of jargonelle pears, amyl- 
acetic ester, isoamylacetate. C,H,,C,H;Q,. 
Molecular weight, 130. Solubilities, insoluble in 
water, miscible in all proportions with alcohol 
and ether. It is a colourless ethereal liquid with 
characteristic odour, and is obtained by distilla- 
tion from amyl alcohol, sulphuric and acetic 
acids. It is used for making celluloid cold 
varnish or zaponlack, a formula for which is— 


Celluloid ‘ 15 g. 
Amyl acetate to . 1,000 ccs. 


This gives a hard, resistant film which can be 
applied cold to negatives. The addition of 
acetone gives a milky film. It is also used in 
the amyl acetate lamp (which see). 

In process work, amyl acetate is used as a 
solvent for celluloid, and the resulting varnish 
is used for stripping instead of collodion. The 
varnish is used in aerograph retouching for 
stopping out, and the amyl acetate for removing 
the varnish after the colour has been applied by 
the aerograph. 


150 grs. 
20 OZ. 


Amyl Acetate Lamp 


AMYL ACETATE LAMP (Fr., Lampe 2 
amylacetate ; Ger., Hefner Lamp) 

A lamp devised by MHefner-Alteneck and 
adopted by the International Congress of Photo- 
graphy in 1889 as the standard light for sensi- 
tometry. The wick should consist of loose 
cotton threads, and be held in a tube of 8 mm. 
(about -32 in.) internal and 8-3 external diameter, 
and of 25 mm. (1 in.) length. The height of the 
flame should be 40 mm. (1°6 in.), and this must 
be gauged by a sight hole and cross wire. Out- 
side the flame, at a distance of 1 cm. (-4 in.) from 
its axis, is a metal chimney pierced with a hole 
4 mm. (‘16 in.) broad and 30 mm. (1:2 in.) long, 
which can be shifted so as to bring it opposite 
the brightest part of the flame. The amyl 
acetate should be free from acetic acid and water, 
and have a constant boiling point of 138° C. 
(280-4° F.). The standard English candle 
1°14 H.K. or Hefner-Kerze. 

The great objections to the amyl acetate lamp 
as a standard photographic light are its spectral 
composition, which is very poor in violet and 
blue rays, and its variability under varying 
heights of the flame (1 mm. or -0q4 in. variation 
in height produces an alteration of about 3 per 
cent.), the influence of aqueous vapour and car- 
bonic acid in the air, and also the state of the 
barometer on the uniformity of the light. (See 
also “* Sensitometry.’’) 


AMYL ALCOHOL (See “ Alcohol.’’) 


AMYLOTYPE (Fr., Amylotypie ; Ger., Amy- 
lotypie) 
A photograph or print obtained by the action 
of light upon vegetable matter or extracts, (See 
** Anthotype.’’) 


ANACHROMATIC 


A name given to certain lenses, mostly of 
French manufacture, which are uncorrected for 
chromatic aberration. 


ANACLASTIC 
clastisch) 


Capable of refracting, or bending, 
light. Dioptrics, that branch of optical science 
dealing with the phenomena of refraction, was 
formerly called anaclastics. 


ANAGLYPH (Fr., Anaglyphe; Ger., Anaglyph) 

The name given to Du Hauron’s stereoscopic 
pictures. A pair of stereoscopic photographs is 
taken and half-tone process illustrations prepared 
from them. The picture belonging to the left 
eye is printed in one colour — say blue; and 
the picture belonging to the right eye is printed 
in another colour, usually red. The two impres- 
sions are superposed, but owing to their stereo- 
Scopic dissimilarity they do not exactly register, 
with the result that a confused effect is produced. 
To observe the pictures stereoscopically, eye- 
glasses (see “ Anaglyphoscope”) are provided. 
If the left eye phase has been printed in 
blue and the right-eye phase in red, the eye- 
piece for the left eye will be ted, and that for 
the right eye will be blue. The eye looking 
through the red glass will observe only the 
phase that has been printed in the blue colour, 
and vice versa. The result is that only one pic- 


(Fr., Anaclastique; Ger., Ana- 


trays of 


28 


Anamorphoscope 


ture or stereoscopic phase reaches each eye and 
the one rightly belonging toit. Further, as both 
images appear at the same place, unison takes 
place in virtue of the laws governing binocular 
perception, and stereoscopic relief is observed. 
The fundamental principle of Du Hauron’s in- 
vention has also been applied to lantern stereo- 
scopic pictures. 


ANAGLYPHOSCOPE 


An appliance or arrangement for the inspection 
of anaglyphs, usually made in the form of eye- 
glasses or spectacles with a red and a green glass, 
or red and blue. Tinted gelatine and other 
transparent materials are also used. Perhaps 
the simplest form consists of a card with two 
circular openings, at a distance apart equal to 
that between the average pair of eyes, over 
which are glued pieces of gelatine of the requisite 
tints. This is simply held up to the eyes in 
viewing the anaglyph, which is then seen in 
stereoscopic relief, 


ANALYSER (Fr., Analyseur ; Ger., Analysator, 
Zerstreuungsprisma) 

A prism of Iceland spar, divided diagonally 
down its long axis, which receives the extra- 
ordinary ray from the Nicol prism (which see). 
The analyser enables the observer to study the 
phenomena of polarised light. It is usually 
mounted in a brass cell above the objective, but 
may be placed above or in the eyepiece. (See also 
“ Polariscope”’ and “ Polariser.’’) 


ANALYTICAL PORTRAITURE 


The taking of several properly adjusted por- 
traits of different persons upon one plate, or the 
printing of several different portrait negatives 
upon one piece of paper; the result is sup- 
posed to give the type of the whole. Better 
known as “ Composite Portraiture” (which see). 


ANAMORPHOSCOPE (Fr., Anamorphoscope ; 
Ger., Anamorphoskop) 


A cylindrical convex mirror for reflecting the 
image of a distorted drawing and restoring it to 
its proper proportions. Concave or convex 
mitrors distort images in a singular manner, and 
produce very interesting effects, Anamorphoses 
constitute particular objects belonging especially 
to the class of experiments relating to cylindrical 
mirrors. They are images made according to 
determined rules, but so distorted that, regard- 
ing them fixedly, only confused strokes can be 
distinguished. When they are seen reflected in 
the curved mirrors, they present, on the contrary, 
a perfectly regular appearance, In other words, 
an anamorphose is a distorted diagram, the cor- 
rected image of which can be seen in the mirror 
of the convex anamorphoscope. It may be said 
that distorted copies of photographs suitable for 
inspection in an anamorphoscope may be pre- 
pared in the following manner: Procure an 
optically worked cylindrical concave mirror large 
enough to reflect a half-plate photograph. Place 
the photograph in a horizontal position upon 
a table, and place the mirror at right angles 
thereto, keeping it vertical. On looking into the 
mirror from a given position, a distorted image 
of the photograph will be seen. This image may 
now be photographed by placing a camera lens 


Anaplanatic 


at the point previously occupied by the eye, a 
position to be discovered by experiment, and 
which will, of course, depend upon the curvature 
of the mirror in use and the focal length of the 
camera lens. The resultant photograph will 
bear no apparent resemblance to the original ; 
but if viewed in a convex cylindrical mirror whose 
curvature corresponds to the curvature of the 
concave mirror, a true copy of the original 
photograph, in miniature, will be seen. The 
order of things may be reversed with equally 
true results. In taking photographs of this 
character it is important so to arrange the 
lighting that the original photograph receives full 
illumination, while the mirror is well shaded. 

A curious effect may be produced by taking 
a photograph with a plate placed very obliquely 
to the axis of a lens or pinhole, the latter being 
preferable. The image is of course terribly 
distorted, but upon being viewed from a position 
similar to that occupied by the lens it will 
appear correct. A portrait painted in this 
style may be seen in the National Portrait 
Gallery, London. 


ANAPLANATIC 
Not aplanatic. The term has been applied 
(incorrectly) to ordinary rectilinear lenses. 


ANASCOPE (Fr., Anascope ; Ger., Anaskop) 


A focusing glass or optical arrangement by 
the aid of which the image on the camera screen 
is seen right way up instead of being inverted. 


ANASTATIC PROCESS (Fr., La _ Photo- 
gvaphie Anastatique; Ger., Anastatisch 
Druck) 

A method of copying line drawings by placing 
a sensitive material with its film side in contact 
with the drawings, and exposing to light through 
the back of the sensitive paper or plate. This 
process, originally invented by J. H. Player, has 
been rediscovered and elaborated by E. E. 
Fournier d’Albe, who has given it the above 
name. As in Playertype, it depends on the 
fact that the light passing through the plate 
or sensitive paper is reflected back to the film 
from the white surface of the plan or drawing, 
whereas the dark lines of the latter reflect 
hardly any light. If plates are used, the photo- 
mechanical kind is best. The exposure is about 
the same as would be required to make a positive 
transparency from an ordinary negative on the 
same kind of plate. A quick-acting developer 
giving contrast is to be preferred, as, for example, 
hydroquinone with caustic potash, or a I in 15 
solution of rodinal. The slight fog that occurs 
in the lines may be removed by a brief immersion 
in a ferricyanide and “hypo” reducer after 
fixing and washing, following this by at least 
half an hour’s further washing. 

A positive instead of a negative may be pro- 
duced by soaking an unexposed dry-plate for 
five minutes in a 10 per cent. solution of potas- 
sium bichromate and allowing it to dry, of course 
in non-actinic light. This is exposed to daylight 
through the glass side, in contact with the draw- 
ing to be copied, and is developed with a dilute 
rodinal solution. The parts which have received 
reflected light from the drawing are rendered 
more insoluble than those parts in contact with 


29 


Anastatic Process 


the darker portions, and the latter in conse- 
quence alone absorb the developer. It follows 
that the lines of the original are developed ont, 
while the background remains white or nearly 
so. The positive is fixed in “hypo” as usual. 
Copies can also be produced by this process on 
bromide paper, and there are many other ways 
in which the process may be applied. It is 
immaterial if the drawing has printing or other 
matter on the back. Distinctive points of this 
process are that no camera or lens is employed, 
and that the copy is exactly the same size as the 
original, 

Anastatic photography must not be confused 
Habe the anastatic lithography process described 

elow. 


ANASTATIC PROCESS OF LITHOGRAPHY 
A process of lithography by which prints, 
particularly old ones, may be treated so as to 
yield a transfer, which may be inked up and 
printed from. The essential features of the pro- 
cess are that the ink of the print is softened and 
made transferable by damping the back of the 
paper with dilute acid; or the print is so treated 
that the ink can be reinforced by rolling it up 
with an ink roller without soiling the paper. 
The usual method, when the print is not too old, 
is to wet the print with a weak solution of nitric 
acid in water. It is then placed face downwards 
on a sheet of polished zinc and passed through 
the press. Sometimes the plate is flooded with 
turpentine, and, after allowing it to stand, the 
surplus is squeegeed off. Then the print is laid 
down before the turpentine has had time to 
evaporate. Another procedure is to float the 
print face upwards on a solution of 1 part of 
sulphuric acid in 20 parts of water. When 
damped through, superfluous moisture is removed 
between blotting-paper, and the print is then 
left in contact with the plate for some time. 
The following is said to be a process employed 
by a Paris firm, who make a speciality of litho- 


graphic facsimiles of old and rare prints. Pre- 
pare a bath as follows :— 
Sulphuric acid . - - 3to5 parts. 
Alcohol A : a Ee 
Water ; 100 a 
The proportions are varied according to 


antiquity of the print, thickness of paper, etc. 
In this solution soak the print from five to fifteen 
minutes, remove, spread face downwards on 
glass, and wash thoroughly in a gentle stream 
of running water. If the paper is heavy, reverse 
the sides, and let the water flow over the print 
as well; remove carefully, and place on a heavy 
sheet of blotting-paper, cover with a similar 
piece, and press out every drop of water possible. 
A wringing machine with rubber rollers is most 
convenient for the purpose. The print, still 
moist, is laid face upward on a heavy glass plate, 
or lithographic stone, and smoothed out. With 
a very soft sponge go over the surface with a thin 
gum-arabic solution, The print is now ready 
for inking, which is done with a lithographic 
roller and lithographic ink thinned with tur- 
pentine. The print is then applied to a zinc 
plate or a lithographic stone, and as many copies 
as desired ‘‘ pulled’’—that is, printed by the 
usual lithographic method. 


Anastigmat 


ANASTIGMAT 

A lens free from the defect known as astigmat- 
ism (see “‘ Astigmatism” and ‘‘ Lens’), Anas- 
tigmatic is the adjective formed from this term. 


ANGLE OF FIELD OR OF VIEW 

The angle subtended by two lines drawn from 
the node of emergence of any lens to the corners 
of the plate in use. As a general rule, when the 
angle of field of a lens is referred to, the extreme 
angle which the lens is capable of covering is 
meant, and it should be clearly stated in all 
cases whether this angle is measured along the 
longest side of the plate or diagonally from 
opposite corners. It will readily be seen that a 
much wider angle can be included in a circular 
picture than in a rectangular one if the full 
diameter of the image circle is taken as the base 
instead of taking the longest side of the plate. 
For example, when using a 6-in. lens which will 
illuminate a 12-in. circle, the extreme angle is 
90°, but the largest rectangular picture (say, 
9+ in. by 7} in.) which could be placed within 
this circle would include an angle of less than 
77°. To cover a plate having a base line of 
12 in, (12 in. by 10 in.) to the corners, an image 
circle of 15:6 in. is required, giving an angle of 
90° along the longest side of the plate. (See also 
*““ View-angles, Table of.’’) 


ANGLOL 


An English trade name for eikonogen (which 
see). 


ANGULAR APERTURE 


A synonym for focal aperture (which see). It 
has no relation to the angle embraced by the 
lens, being a measure of rapidity only. The 
statement that a lens has a large angular aperture 
means in simple language that it is very rapid 
in its action. 


ANHYDROUS (Fr., Anhydre; Ger., Wasserfret) 


A term applied to chemicals when deprived 
of water; literally, not containing water. 
Anhydrous sodium sulphite is the most widely 
used anhydrous salt in photography. It is said 
to keep better in an anhydrous state than when 
crystallised. The anhydrous salt is double the 
strength of the crystallised salt, so that 1 part 
of the former may at any time be replaced in 
a formula by 2 parts of the latter, or vice versa. 
Anhydrous chemicals are not so popular in 
England as in many other countries. - 


ANILINE (Fr., Aniline ; Ger., Anilin) 

Synonyms, aniline oil, phenylamine, amido- 
benzene, amido-benzol. C,H,NH,. Molecular 
weight, 93. Solubilities, insoluble in water, misci- 
ble in all proportions with alcohol and ether. 
It is poisonous, the antidotes being the use of 
the stomach pump and emetics. Its sole use is 
in the now obsolete aniline process (which see), 
and as the starting-point for the manufacture of 
numerous artificial colouring matters. It should 
not be confused with aniline, or coal-tar, 
colours (which see). 


ANILINE, OR COAL-TAR, COLOURS 


Under this generic name are included all the 
artificial colouring matters or dyes, some of 


30 


Animals 


which are of great interest photographically, 
either from their sensitising properties or their 
uses as colour screens or filters. Others, again, 
are used for tinting prints, transparencies, etc. 
It would be impossible to give information with 
regard to all the dyes, but the principal ones 
are briefly dealt with under their respective 
names, (See also ‘‘ Orthochromatism,” “ Fil- 
ters,’”’ “ Colour Sensitisers,”’ etc.) 

In process work, aniline dyes are extensively 
used, especially in three-colour reproduction. 
They are either applied to the plate by bathing, 
or by adding to the emulsion as in the collodion 
emulsion process. For the latter they are also 
sometimes flowed over the plate before exposure. 
Attempts have also been made to bathe wet 
collodion plates, but the process has not 
come into commercial use. Methyl violet is an 
aniline dye that is largely used for dyeing the 
fish-glue image in order to make it visible during 
development. The dyes are also much used 
for making colour filters, either by staining 
gelatine and collodion films and allowing them 
to dry (dry filters), or as aqueous or alcoholic 
solutions, which are contained in glass cells and 
placed in front of or behind the lens. 


ANILINE PROCESS 

A process patented on November 11, 1864, 
by W. Willis, of Birmingham, for reproducing, 
without a negative, drawings made on tracing or 
other transparent paper. It is cheap, and the 
results are fairly permanent, but it has never 
come into general use. Paper is prepared with 
a solution of potassium (or ammonium) bichrom- 
ate, 30 grs.; dilute phosphoric acid, 60 minims; 
water, I oz,—the paper being brushed over with 
the mixture. When dry, a print is obtained by 
exposure to daylight under the drawing on trans- 
parent paper. It is then developed by exposure 
to the fumes of 1 part of aniline dissolved in 
16 parts of benzole, sprinkled upon blotting- 
paper, and placed in a shallow box, the exposed 
paper being pinned to the inner side of the lid. 
When fully developed the picture is washed and 
placed in water acidulated with 1 per cent. of 
sulphuric acid and again washed. ‘The finished 
print is of a bluish-black colour. This process is 
suitable for copying plans, etc., other methods 
being the “Blue Print Process,” “ Ferrigallic 
Process,”’ etc. etc. 


ANIMALCULAE TANK (Fr., Cuvette des ani- 
malcules ; Ger., Microskopischer Tierchen- 
behilter) 

A shallow glass-sided tank for use as a slide 
with the projection microscope and optical 
lantern, in order to show animalcule and small 
water insects on the screen. A good temporary 
substitute is made by clamping together two 
strips of glass, with a semicircle or ring of india- 
rubber between them to form a cell. 


ANIMALS, PHOTOGRAPHY OF 

This branch of photographic work is one that 
has received increasing attention as improve- 
ments have been made in lenses, plates, appara- 
tus, and special devices. The reflex camera and 
the telephoto lens, especially, have been effective 
helps to the natural history photographer. Animal 
photography may be roughly divided into three 


Animated Photography 


sections: (a) that of domestic animals—the 
horse, cow, sheep, dog, cat, etc. ; (b) that of wild 
animals in their natural habitat ; (c) that of wild 
animals in captivity. 

In the case of wild animals in their native 
haunts, a very limited amount of work may be 
done with the ordinary apparatus; still more 
may be accomplished by the use of telephoto 
lenses; while a good deal has been done by 
special arrangements by means of which animals 
have been made to photograph themselves, so 
to speak, by flashlight. 

The methods of dealing with domestic animals, 
and with wild animals in captivity, are practically 
identical. The work is greatly facilitated by the 
use of a reflex camera; a lens of fairly long focus 
in relation to the plate, and of large aperture; a 
rapid plate; and a shutter working as quietly 
as possible with high efficiency and capable of 
good speed. It is advisable to know something 
of the animal to be dealt with, especially its 
characteristic poses and movements. ‘The reflex 
camera enables the worker to keep the animal 
accurately in focus and in position on the plate, 
and to make the exposure at the most suitable 
moment. The use of a large stop makes full 
exposute possible even at high-shutter speeds, 
and also bestows the important advantage of 
being able to keep the background diffused while 
the animal itself is sharply defined. 

Selective focusing and a_ suitable lighting 
of the animal itself are important factors in 
obtaining an impressive result. It must be 
remembered, however, that even when the back- 
ground is diffused its character and suitability 
must be carefully considered. If, for example, 
it contains many points of bright light, these 
may be exaggerated into “‘ blobs” that are 
unsightly and irritating. Another thing to 
avoid is the use of a short focus lens at close 
quarters, especially when taking an animal 
“head on,” the result being an exaggeration of 
the head and a dwarfing of the body. It is 
generally advisable, particularly in the case of 
small animals, to hold the camera low down. 
An effort should be made in the case of wild 
animals in captivity to keep out of the picture 
any railings, network, or other evidence of their 
not being in their natural haunts. 

When the camera used focuses to scale, and 
a reflex camera is not available, failure is mini- 
mised by not attempting work at very close 
quarters, but rendering the animal on a smaller 
scale and afterwards enlarging the result. The 
most noticeable drawback to this procedure is 
that the surroundings and background are ren- 
dered too sharply, and so compete in importance 
with the animal itself. (See also ‘‘ Birds, Photo- 
graphy of,” and “‘ Zoological Photography.’’) 


ANIMATED PHOTOGRAPHY (See “ Kine- 
matography.”’) 


ANIMATOGRAPH 


ANIME (See “ Gums and Resins.’’) 


ANOMALOUS DISPERSION (Fr., Dispersion 
irveguitére ; Ger., Abweichende Zersireuung) 


As a rule, light rays of short wave-length are 
tefracted more than those of long wave-length 


(See ‘*Kinematograph.”’) 


Anthrakotype 


when passing from one transparent medium to 
another of different density. With some refract- 
ing media, however, this law is departed from to 
a certain extent. When this occurs it is known 
as anomalous dispersion. 


ANTHION 


A -trade name for potassium persulphate 
(which see). 


ANTHOTYPE 

An obsolete “nature printing’? process in- 
vented by Sir John Herschel and founded upon 
the sensitiveness of juices of plants. Chevreul 
and Hunt also experimented in the same direc- 
tion, The expressed juices, and alcoholic or 
watery infusions of certain flowers, more par- 
ticularly papaver rh@as and corchorus japonica, 
were spread on paper and printed upon under 
a negative. Herschel found that the most 
sensitive colour was the yellow tint of the 
japonica, and that the blue tincture of the 
double purple groundsel completely bleached in 
the sunshine. According to his original instruc- 
tions, published in 1842, the petals of fresh and 
well selected flowers are bruised to a pulp in a 
marble mortar, either alone or with a small 
quantity of alcohol, and then are squeezed 
through fine linen. The paper to be treated is 
moistened at the back with water, by sponging 
and blotting off, and pinned to a board, moist 
side downwards. ‘The alcoholic tincture (mixed 
with a very little water if necessary) is then 
applied with a brush, in strokes from left to 
tight. Then with a sweeping movement carry 
the strokes up and down so as to cover the 
paper completely and leave no spaces. The 
paper is dried quickly, over a stove or otherwise. 
Papers so prepared generally require an exposure 
under a negative of about three or four weeks, 
and the pictures are not permanent. Herschel 
found that similar effects could be produced by 
light on the gums, resins, and residues of essen- 
tial oils, when thin films were spread on metal 
plates ; also that a paper coated with an alcoholic 
solution of guaiacum, and placed in an aqueous 
solution of chlorine, acquired a beautiful blue 
colour, and could be used for copying engravings. 
All images by these processes quickly fade, and 
ate of no value except as curiosities while they 
last. (See also ‘‘ Nature Printing.’’) 


ANTHRAKOTYPE (Fr. and Ger., A nthrakotypie) 

A dusting-on process, suitable for copying 
tracings or line drawings, first described by Dr. 
Sobacchi, and elaborated by Captain G. Pizzi- 
ghelli. Paper is coated with, say, a 10 per cent. 
solution of gelatine, and when dry is sensitised 
in a solution of potassium bichromate of about 
5 per cent. strength. After again drying, the 
paper is exposed under a tracing or other suit- 
able positive until the ground assumes a light 
brown colour, on which the lines are faintly 
visible in pale yellow. The print is then soaked 
in slightly warm water for about two minutes, 
blotted off, and dusted over with a pigment. 
The latter may be any finely powdered colour, 
lampblack being suitable. The pigment adheres 
to the unexposed parts (that is, the lines of the 
drawing), which are swelled by the water ; while 
the portions on which light has acted are ren- 


Anthraphotoscope 


dered insoluble, and take only slight traces of 
the colour. When dry, any of the pigment 
adhering to the exposed parts is removed care- 
fully with a damp sponge. 


ANTHRAPHOTOSCOPE 
An incorrect form of the word “‘ anthrophoto- 
scope ’’ (explained below). 


ANTHROPHOTOSCOPE (Fr., <Anthrophoto- 
scope; Ger., Anthrophotoskop) 

A kind of photographic peep-show, patented 
in 1867 by Dr. Isaac Rowell and Francis E. 
Mills, of San Francisco. Portrait photographs 
are carefully cut out from their backgrounds and 
placed in front of substituted backgrounds 
attached to an inclined plane, diverging upward 
from the plane of the portrait and intersecting 
the latter at the feet. By this arrangement the 
foreground is slightly nearer to the observer 
than the middle distance, while the distance is 
still further off, so that when viewed with both 
eyes through a large magnifying lens of long 
focus, the illusion of perspective and at least an 
imitation of stereoscopic relief are obtained. By 
means of a small toothed wheel the pictures may 
be arranged into groups at pleasure, and the 
scenery in the background may also be varied 
as desired, 


ANTI-CURLING FILMS 


Rollable or flat films which do not curl during 
developing and drying. The makers prevent 
cutling by coating the back of the film with 
gelatine, or other substance, to counteract the 
curling properties of the gelatine on the sensitive 
side of the film. Previous to the introduction 
of the above films, it was customary to soak 
ordinary films, after developing, fixing, and 
washing, for a few minutes in a solution of 1 part 
of glycerine to 40 parts of water, and after- 
wards to dry. This solution checks curling, 
but keeps the film slightly moist, and at times 
leads to stains and fading. 


ANTIDOTES (See ‘Poisons and Their Anti- 
dotes.’’) 


ANTI-HALATION PLATES 


Dry plates coated on the back (plain glass 
side), or otherwise prepared, to prevent light 
being reflected to the film when in the camera. 
Such reflection causes the defect known as 
halation (which see). Dry plates made of 
green glass instead of white glass are said to 
prevent halation perfectly (no backing being 
necessary), but they are not articles of com- 
merce. 

The earliest forms of anti-halation plates were 
made by staining the film. W.E. Debenham, 
in 1891, used saffron and logwood, but these 
increased the exposure. Weir Brown advocated 
dipping plates in ammoniacal erythrosine. A. 
Haddon suggested a thin coloured substratum, 
and T. Bolas the coating of ruby glass with emul- 
sion and then stripping the film, also the addition 
of some neutral salt to the emulsion. Anti- 
halation plates with a coloured substratum were 
for a time articles of commerce, but the term now 
generally refers to plates backed in the ordinary 
way. (See also “ Backings, Plate,’’) 


32 


Antimony Sulphide 


ANTILUMIN 

A special paper impregnated with a ruby or 
orange dye and rendered semi-transparent. It 
is used for covering dark-room windows and 
lanterns, to make the light “‘ safe.’’ 


ANTIMONY PROCESS (Fr., Photographie 
a lantimoine ; Ger., Spiessglas-Druck) 

A printing process discovered by Francis 
Jones, of the Manchester Grammar School, in 
1876. When the gas stibine, or antimonietted 
hydrogen (SbH,), is passed through a glass tube 
containing sulphur, in the presence of sunlight, 
a decomposition takes place, resulting in the 
formation of the orange antimony sulphide :— 


Stibine Sulphur Antimony Sulphuretted 
Sulphide Hydrogen 


Since no change occurs in the dark, it was found 
possible to utilise the reaction for photographic 
purposes. Ordinary writing paper may be 
treated with a solution of sulphur in carbon 
disulphide and the solvent allowed to evaporate, 
the loose grains of sulphur being then gently 
brushed off the surface with a tuft of cotton- 
wool. A special printing frame is used, having 
a tube led into the back, so that the gas may be 
conveyed into the felt with which this is lined 
in order to impregnate the paper. A fern, a 
piece of lace, or other suitable object having been 
placed in the frame and the paper laid over it, 
the frame is exposed to sunlight, and connection 
is made with the gas. A print of an orange 
red colour is quickly produced, the image con- 
sisting of permanent metallic sulphide imbedded 
in free sulphur. No fixing is required, the gas 
being simply disconnected when printing is 
sufficiently advanced. The operation should be 
carried out in the open air, care being taken not 
to inhale the fumes, which are poisonous. To 
obtain the gas, a small quantity of a solution of 
antimony trichloride (butter of antimony) is 
added to any hydrogen generating apparatus, as, 
for example, a Woulff’s bottle furnished with a 
thistle funnel and a delivery tube, and contain- 
ing dilute sulphuric acid and granulated zinc. 
The emerging gas then consists of a mixture of 
antimonietted hydrogen and hydrogen. It is 
advisable to dry the gas by passing it through 
poate chloride tube before leading it into 
the printing frame. Although of considerable 
interest, this process appears to have certain 
disadvantages, which have hitherto prevented 
its use by the practical worker, not the least 
of these being that the silver image of a negative 
begins to be affected by the sulphur after several 
impressions have been taken. 

In process work, there is an antimony process 
which consists in blackening a zine plate with a 
solution of antimony chloride in order that an 
image transferred to the plate may show up after 
the plate has been slightly etched. This allows 
of an artist working on the plate by stopping-out 
for re-etching. 


ANTIMONY SULPHIDE (Fr., Sulfure d@anti- 
moine ; Ger., Schwefelantimon) 
Synonyms, antimonous sulphide, black anti- 
mony. Sb,S;. Molecular weight, 336. Solu- 
bilities, insoluble in water, soluble in hydro- 


Antiphotogenic 


chloric acid. It is poisonous, the antidotes being 
the use of the stomach pump and emetics. It 
takes the form of a greyish black powder or 
steel-grey metallic masses, occurring native. It 
is occasionally advised as an admixture with 
magnesium powder for flashlight work, but 
its use is not to be recommended as the products 
of its combustion are poisonous. 


ANTIPHOTOGENIC (Fr., 
Ger., Anttphotogentsch) 
Opposed to photographic or photo-chemical 
action; non-actinic. 


ANTIPLANAT, 
LENS 

A lens introduced by Steinheil, of Munich, in 

1881, and made in two intensities, f/3 for por- 

traits A and f/6 for general work B. They differed 


A ntiphotogénique ; 


OR ANTIPLANATIC 


B. Steinheil Antiplanat 
F/6 


F/3 


from most contemporary lenses inasmuch as they 
were composed ofa positive front anda negative 
back lens. In the more rapid form the anti- 
planat may be regarded as a triple combination 
lens, while in the slower one it is a doublex. 


ANTIPYR 
An American trade name for formaline. 
ANTISEPTICS (Fr., Antiseptiques; Ger., 
Faulnisswidrig Mittel) 
Agents used to prevent putrefaction. They 


find but very limited use in photography. 
Thymol or phenol is used for gelatine emulsions, 
and salicylic acid in one or two aqueous solutions 
which have a tendency to form fungoid growths. 


ANTISPECTROSCOPIC (Fr., Antipectrosco- 
pique ; Ger., Antispectroskopisch) 

An optical term applied to a lens to signifiy 
that it does not split up white light into its con- 
stituents. Achromatic (which see) has the same 
meaning. 


APERTOMETER (Fr., Ouverture métre; Ger., 
Oceffnungmesser) 


An instrument for measuring the numerical 
aperture of a lens or objective. Of those forms 
used in photomicrography, the best was devised 
by Abbe, consisting of a semicircular glass plate 
with the various apertures figured on the outer 
edge. The straight edge of the glass is bevelled 
to an angle of 45°, and in the centre of the bevel 
is a metal disc pierced with a small hole. The 
lamp must be placed opposite and in line with 
this hole. The objective to be tested is focused 
on the metal edge of the hole, the draw-tube is 
removed, and a low-power objective, which 
forms part of the apparatus, is screwed into the 
lower end. The draw-tube with this second 

3 


33 


Aphengescope 


objective is replaced, and the auxiliary lens is 
focused by means of the draw-tube upon the 
back of the objective which is being tested, by 
sliding the draw-tube up and down till the images 
of two metal pointers on the outer edge of the 
apertometer are sharply defined. A band of 
light should be seen across the field, and the 
pointers are moved till they just reach the edge 
of the luminous band, where it disappears from 
the field of view. The readings given by the 
outer edges of the metal pointers are added 
together, and the half of the sum gives the 
numerical aperture. 

Cheshire’s is an inexpensive and fairly accur- 
ate apertometer, consisting of a glass disc with 
concentric rings on the under surface. The 
objective is focused on a mark in the centre of 
the plate, and the eyepiece is then removed. 
The observer looks down the tube and notes 
the number of rings which are visible on the 
back lens of the objective. The value of each 
ring is O-1 numerical aperture (N.A.), and the 
total gives the N.A. of the objective. 


APERTURE 

The diameter of the beam of light admitted 
by a lens, which may or may not coincide with 
the diameter of the “stop” or “ diaphragm ”’ 
(which see). A lens which can be used with a 
comparatively large stop, or no stop at all, 
without showing want of definition or other 
defects, is said to be “rapid,” and to havea 
“large working aperture.” When there is no 
stop in the lens at all, it is {said to work at 
“open aperture” or “full aperture.” 


APHENGESCOPE (Fr., Mégascope, Aphenge- 
scope; Ger., Aphengeskop, Wunderkamera 
fiir Undurchsichiige) 

In the aphengescope or opaque lantern, also 
sometimes called the megascope, the images are 
projected upon the screen by reflection instead 
of by transmitting the light through transpar- 
encies. The first magic lantern of this nature 
appears to have been invented by Euler, the 
mathematician, and was described in his ‘‘ Letters 
to a German Princess.’ In his letter to her of 


— SP 


A. Euler’s Aphengescope 


January 8, 1762, he gives diagram A, and says 
that he had the honour of presenting her with 
one of the lanterns six years previously. 

The object to be optically projected was placed 
in the back of the lantern at B, and opposite it 
in a sliding tube in the front of the lantern was 
the projection lens a. It contained two side 
wings, with lamps and mirrors to illuminate the 
object. In the ‘“‘ Encyclopedia Metropolitane ”’ 


Aphengescope 


is a plan of this or another lantern by Euler for 
the projection of opaque objects. Prior to 
Euler’s invention it seems that the rays of the 
sun were used to illuminate an object the image 
of which was then thrown upon a screen. Really 
practical instruments, however, were mot con- 
structed until about the year 1839, when Mr. 
Longbottom used the oxyhydrogen light in 


B. Diagram of Single Lantern Aphengescope 


conjunction with opaque lanterns, with which 
he gave exhibitions at the old Polytechnic 
Institute, London. Twenty years later Mr. 
Chadburn, of Liverpool, obtained a patent for 
a lantern of the opaque class, in which he also 
used oxyhydrogen illumination. 

In all aphengescopes great illuminating power 
is necessary if a large picture upon the screen is 
desired. Fair results may be secured by using 
an ordinary optical lantern for the purpose, 
arranged as shown in B, in which 4 is the objective 
lens, 1, the lantern containing the source of 
illumination, and B the space in which to place 
the picture or object to be projected. When very 
large pictures are needed two lanterns may be 


U 


D. Foote’s “Polyopticon” Aphengescope 


used, as indicated in illustration C. The double 
suurce of illumination makes the picture or object 
B very bright, and the lens a transmits a brilliant 
image to the screen. 

A most ingenious form of aphengescope was 
invented some years ago by an American, Dr. 
Foote, of New York, who termed his instrument 
the ‘ Polyopticon Wonder Camera.” Great 
illumination is secured by the use of a concave 
mirror M, in illustration D, gathering up all the 
rays from a lamp at D, and reflecting on to the 
picture at B; the objective lens is shown at A, 


34 


Aphengescope 


The reflector is pierced for the lamp-chimney, 
and also for the object glass. The apparatus 
may be compared to a huge egg, having one end 
sliced off obliquely, against which opening the 
picture to be projected is placed. There is no 
condenser needed, and although the size of the 
projected picture is necessarily of limited dimen- 


C. Diagram of Double Lantern Aphengescope 


sions, it is very popular in the United States 
for projecting enlarged views of cartes, coloured 
lithographs, etc., of small size. Illustration E 
represents a more recent form of aphengescopic 
attachment. The objective lens is at a, the object 
or picture to be projected at B, and a mirror at 
M, the latter serving to divert the rays coming 
from the illuminant p from a horizontal into a 
more or less vertical direction. A biunial form 
of this apparatus is shown in illustration F. Two 
lanterns are used, and two mirrors M concentrate 
the light to a common point B, where the picture 
or object to be projected is situated. Naturally, 
a much brighter picture is the result, and 
accordingly a much larger image upon the screen 
is permissible. The aphengescope suggested by 
Mon. Trouvé, and introduced by Mon. Molteni, 
of Paris, was termed “1’Auxanoscope,” and the 


E. Recent Type of Aphengescope with 
Adjustable Diverting Mirror 


simplest form of this apparatus is provided with 
a lamp on each side of the objective. The 
incandescent electric lights are fixed in tubes, 
the ends of which are provided with reflectors, 
with a hole in each to allow of the insertion of 
the conducting wires. In the pattern having 
three illuminants, two are used as just described ; 
while a third, at the back, is utilised for trans- 
mitting light direct when inserting an ordinary 
transparency in the groove provided. 

Devices on the same principle have lately been 
used for projecting the image of the dial of a 
watch upon the ceiling so that a person lying 
in bed may switch on the lamp and see the time. 


Aplanat 


A practicable form of aphengescope for attach- 
ment to optical lanterns is hexagonal in plan, 
and is made of either wood or metal. At the 
back are two doors permitting of one object 
being shown while another is being prepared. At 
the front are three holes, the central one having 
a flange to receive a lantern objective of long 
focus and large diameter, and the side holes 
being bushed with brass tubing to receive the 
draw-tubes of two lanterns. The object to be 
shown is placed in the aphengescope behind the 
objective. 

Modern lighting facilities are responsible for 
the recent revival in opaque lanterns. Incan- 
descent gas, incandescent electric lamps, and the 
more powerful electric arc, supply all that is 
necessary with regard to illumination in order 


F. Biunial Form of Aphengescope 


to procure brilliancy of image upon the screen. 
But with improved lighting facilities comes the 
possible evil of overheating the subject, and 
consequently damaging the originals. One pre- 
caution against this evil suggests itself in the 
form of an alum tank, interposed between 
illuminant and subject, which performs the 
function of absorbing heat rays without 
unduly interfering with the course of the illu- 
minant rays. Such a device has often been used 
in conjunction with lanterns when projecting 
transparencies, especially when the slide is 
required to remain stationary for any length of 
time. Moving panoramic pictures for the 
aphengescope have been suggested, and in this 
case it may not be necessary to introduce an 
alum tank or heat absorber; but for lecture 
purposes, when the picture is fixed for a con- 
siderable period, an absorber is a useful adjunct. 
“‘Mirroscope”’ is the name given to arecent form 
of aphengescope, and it is designed separately for 
electric, acetylene, and incandescent gas light. 


APLANAT 

A lens sufficiently well corrected for chromatic 
and spherical aberrations to define well at a large 
aperture. The name is now usually applied to 
lenses of the rapid rectilinear type, although a 
special lens called a ‘‘ rapid aplanat ” (f/6°5) was 
introduced by Steinheil in 1893. This somewhat 
resembled the antiplanat of the same maker in 
having a positive front and negative back lens, 
but consisted of five glasses. 


APLANATIC 

Capable of working at full aperture, a term 
first applied to photographic lenses by Thomas 
Grubb, of Dublin, who introduced an “ aplan- 
atic landscape lens.” 


APLANATISM 
The quality of being aplanatic. 


35 


Arabic, Gum 


APOCHROMATIC (Fr., Apochromatique ; Ger., 
A pochromatisch) 


A term applied to lenses in which light of more 
than two colours is brought to a focus. Inthe 
ordinary achromatic construction, the green and 
yellow rays near the D line in the spectrum and 
the violet-blue rays near G are combined; but 
in the apochromatic lenses the red rays also 
come to a focus on the same plane. This quality 
is invaluable for three-colour work, as images 
taken through blue, green, and red screens are of 
equal size. 

In process work, apochromatic lenses are 
specially suitable for use in three-colour repro- 
duction. The term is one specially used by 
Carl Zeiss to describe lenses for colour repro- 
duction; for example, the ‘‘ Apochromatic 
Planar ’”’ and “ Apochromatic Tessar.’ 


AQUA FORTIS (Latin) 

Weak nitric acid. The term was once uni- 
versally used by chemists for nitric acid, whether 
dilute or not. 


AQUA REGIA (Latin) 

So called because it dissolves the noble 
metals; a mixture of 3 parts of nitric acid and 
1 part of hydrochloric acid. It is used for dis- 
solving gold and platinum, as, for example, 
when making gold chloride, the metals being 
insoluble in the separate acids. Its solvent 
action depends upon the fact that it contains 
free chlorine, liberated by the oxidizing action 
of nitric acid upon the hydrogen of the hydro- 
chloric acid. 


AQUA VITAE (Latin) 
An old name for alcohol (which see). 


AQUARELL PROCESS 

A combination of half-tone and chromo- 
lithography for colour printing, practised 
in Germany. Also known as aquarell fac- 
simile reproduction, aquarell imitation, and 
aquarell gravure. The last-mentioned is 
really a combination of colour plates with 
collotype. 


AQUATINT (See “‘ Gum-bichromate Process.’’) 


AQUATINT ETCHING PROCESS (Fr., Aqua- 
tinte; Ger., Aquatint Manver) 

An old method of forming a ground, or tint, 
for etching on copper. Resin is dissolved in 
alcohol, the proportion of the latter determining 
the firmness or coarseness of the grain, and this 
solution is poured on the polished copper plate. 
As the alcohol evaporates the resin reticulates 
into a granular structure. The plate is slightly 
etched, and then certain parts are stopped out 
corresponding to the tones of the picture. 
Further etchings and stoppings out follow until 
the complete picture is formed in graduated 
tones. Usually the plates are printed from by 
the intaglio method, but the method has also 
been applied in connection with photo-processes 
for typographic colour work. 


AQUATINT, PHOTO (See “ Photogravure.’’) 
ARABIC, GUM (See “ Gums and Resins.’’) 


Arabin 36 


ARABIN (Fr., Acide gummic) 

The pure, soluble principle of gum arabic, and 
existing in different proportions in different 
samples. In good Soudanese gum the proportion 
of arabin is between 78 and 80 per cent.; in 
Turkey gum about 40 per cent. It is used in 
the arabin gum-bichromate process, under which 
heading a method of preparing arabin is given. 


ARABIN GUM-BICHROMATE PROCESS 


A gum-bichromate printing process, worked 
out by Nelson K, Cherril, and published in June, 
1909. To prepare the arabin, a quantity of 
best Soudan gum arabic is sifted through a 
40-mesh sieve. Place in a quart earthenware 
jar 150 ccs. of water, 74 ccs. of pure hydrochloric 
* acid, and then sift into the mixture, stirring the 
while, 100 g. of the powdered gum. Keep the 
whole at about 120° F. (about 49° C.), and 
stir frequently until solution is complete. Cool 
and add 600 ccs. of the best methylated alcohol, 
free from petroleum, and stir for half an hour or 
so, or until the arabin is thrown down as a white 
precipitate and has lost all stickiness or gum- 
miness. Filter through two thicknesses of 
cheese-cloth, gather the arabin in the cloth into 
a ball, and squeeze it well, place it in a small 
jar, cover with new spirit, stirring it and break- 
ing it up well, and leave for several hours until 
the spirit has absorbed all the water. Squeeze 
again in cheese cloth, then put the arabin in a 
towel and squeeze it in a press, with as heavy 
pressure as possible. Break up the cake formed, 
to allow the remaining alcohol to evaporate, with 
gentle heat; then break the remaining lumps in 
a mortar and dry until all is a dry, gritty powder. 
The formula in the English system would be 
roughly as follows :— 


Water ; : ; 54 oz. 
Hydrochloric acid . ; we 27 mins. 
Powdered gum ‘ : 1540 grs. 
Methylated alcohol . 21 OZ. 


To prepare synthetic gum, take 20 g. of 
arabin, 20 g. of heavy magnesium carbonate, 
and from 40 ccs. to 75 ccs. of water, according 
to the thickness of the solution preferred for 
coating. This formula in English is — 


Arabin . : , : . 308 ers. 
Magnesium carbonate SOR Ss, 
Water . ; : . 14 to 2} oz. 


When mixed, stir occasionally until the froth 
subsides, then filter through muslin. _ 

To prepare the pigment, lampblack is used ; 
wash it with repeated doses of mixed ether and 
acetone until all fatty, gummy matters are 
removed ; or, preferably, burn small pieces of 
camphor slowly under a piece of porcelain—say 
the bottom of a porcelain developing dish. 
Scrape off the soot with a palette knife into a 
test-tube and wash with mixed ether and 
acetone until these solvents come away with 
only slight discoloration. Pour off as much 
as possible without losing the black, and dry 
by stirring the test-tube in hot water, keeping 
the water from the pigment. When dry, the 
tube is inverted, and the black will fall out freely. 
A special lampblack, known as No. 4, has been 
prepared for this particular process. To mix 
the gum and pigment for coating upon paper, 


Arc Lamps 


it is necessary to experiment with the particular 
paper to be used, taking a normal temperature 
—say 95° F.—for the developing water and a 
normal time—say forty-five minutes—for devel- 
opment. The mixture must be such as will just 
soak clean from the paper in the development 
time. With too little gum the pigment soaks 
into the paper; with too much, it washes away 
before development is complete. In practice it 
is best to make up an under-gummed and an 
over-gummed ink, and experiment with these 
will show the proportions for any paper. For 
instance, Cherril recommends the making of one 
ink containing gum in the proportion of 20 arabin 
to 75 water, and the other in the proportion of 
20 to 45 of water. If both these are pigmented 
in the same proportion as to quantity—that is 
to say, about 400 to 500 mm. of lampblack to 
each 10 ccs., the one will be found to give too 
much penetration to Joynson’s or Rive’s paper, 
and the other too little; a mixture of the two 
will be found to give a good result. The 
mixture is sensitised just before use by an 
addition of an equal volume of bichromate 
solution made by adding 15 g. (230 grs.) of 
ammonium bichromate to 100 ccs. (34 oz.) of 
water; dissolve by heat, and neutralise by stir- 
ring in a little chalk, decanting when effer- 
vescence ceases and the solution settles. The 
paper to be used is brushed over thinly with the 
freshly-mixed gum and bichromate, the brush 
marks being obliterated by crossing and recross- 
ing the strokes. After drying, the paper is 
ready to be exposed. Exposure should be by 
actinometer after the manner of carbon, and 
the paper is much more sensitive than the 
average gum-bichromate paper prepared by 
other processes. If the development of a print 
from an ordinary negative is complete in about 
forty-five minutes in water at a temperature of 
95°F. (35°C.), the result will be perfect. Develop- 
ment may be performed in a vertical tank by 
floating face downwards on the water, only 
“controlling” in the usual manner, (For par- 
ticulars of gum work in general, see ‘“‘ Gum- 
bichromate Process.,’’) 


ARAGO, DOMINIQUE FRANCOIS 

An eminent French astronomer and physicist 
(b. 1786, d. 1853), to whom Daguerre showed and 
explained his earliest results. Daguerre’s dis- 
covery was communicated to the Paris Academy 
of Science by Arago on December 7, 1839, and 
it was on the latter’s recommendation that 
the French government awarded Daguerre a 
life pension of 6,000 francs, on condition that he 
published the process. 


ARC LAMPS (Fr., Lampes @ arc ; Ger., Bogen- 
lampen) 

Lamps in which a powerful light is obtained 
by passing an electric current through a pair of 
slightly separated carbon pencils, Where the 
current is interrupted by the gap an intensely 
brilliant arc is created. Arc lamps are of two 
principal kinds : (a) open, in which the carbons 
are exposed to the air, and (b) enclosed, in which 
the carbons are almost hermetically sealed in a 
glass-covered case, and burn in a mixture of 
carbon monoxide and nitrogen formed by their 
own combustion. The enclosed type is coming 


Arc Lamps 


to be preferred, on account of its increased 
actinic power, due to its larger arc, the greater 
Te dpe of violet rays, and the fact that the 
ife of the carbons is much longer, owing to the 
practical absence of air, and consequently slower 
combustion. Some excellent open-type arc 
lamps are, however, obtainable, in which several 
pairs of carbons are used; these obviously yield 
a more powerful light than the single carbon 
pattern. 

The arc light is employed in studio portraiture, 
ptinting, copying, enlarging, and photomicro- 
graphy, also in the optical lantern and cinemato- 
graph. 

In studio work the lamp should be supported 
on an adjustable tripod or bracket, so that it 
may be raised as high as 8 ft. or 9 ft. or lowered 
at will. The direct light of the arc is liable to 
produce hard lighting and heavy shadows; and 
it is therefore advisable either to cut this off by 
a small opaque disc placed in front of the carbons 


AA 


\ 


‘ 


A. Open Type Arc Lamp, with 
Diffusing Screen, etc. 


B. Enclosed 
Arc Lamp 


and to use only the light obtained from an 
umbrella reflector or screen at the back of the 
lamp, or, as an alternative, to use a translucent 
diffusing screen of muslin or tracing cloth in 
front of the lamp. Sometimes these two plans 
are combined. A illustrates the use of a diffusing 
screen C with the Boardman multi-carbon arc 
lamp (open type). The metal shield D screening 
the direct light of the arcs will be noticed, and 
also the large umbrella reflector E. B shows 
an extensively-used pattern of enclosed arc (the 
‘“‘ Westminster ’’) designed for general photo- 
graphic use. For low studios, a reversed 
model is made, having the arc chamber on top 
instead of beneath. Whatever kind of lamp 
is employed, the lens must be shielded from the 
direct rays by means of a projecting hood. 

For printing, the lamp should not be too 
near the frames, a good average distance 
being 2ft. or 3 ft. Various stands are obtain- 
able to support a number of frames in circular 
tiers, the lamp being suspended in the centre. 


37 


Archer 


In lantern and cinematograph work the open 
arc at present holds the field, though the enclosed 
atc is coming into use. Lantern arc lamps are 
so designed as to economise space, and are fitted 
to a sliding tray. A model having the carbons 
at a right angle is claimed to give a better and 
more direct light, and to take up less room than 
those types in which the carbons form a very 
obtuse angle with each other. 

In process work, arc lamps play an important 
part, practically all work being done by electric 
light, because of its uniformity and the certainty 
of the exposures as compared with daylight. 
The “‘open” arc has been almost entirely super- 
seded by the “enclosed” arc. For copying, 
a pair of lamps is usually employed taking 
about 10 amperes, though for large work four 
lamps may be necessary. The lamps are 
enclosed with semi-cylindrical reflectors, which 
are whitewashed inside. For colour work 15 
ampere lamps are frequently adopted, and 
coloured flame carbons utilised to aid the expo- 
sure through the colour filters. Red flame car- 
bons, for instance, are found beneficial with the 
red filter for the blue printing plate. Search 
lights of high amperage are also employed in 
some studios for securing very powerful illumin- 
ation. For printing on the metal, lamps of 
from 15 to 20 amperes are employed. Arc 
lamps for process work are usually run in 
‘*‘parallel’?; and a high voltage—2oo0 volts or 
more—is preferable with enclosed lamps so as to 
obtain about 140 volts across the arc, by which 
means a long flaring arc of great actinic power 
is obtained. 


ARCHER, FREDERIC SCOTT 

Born at Bishops Stortford, 1813, died in Lon- 
don, May, 1857. He invented the wet collodion 
process in 1848, and published working details in 
The Chemist, dated March, 1851, his own 
‘Manual of the Collodion Photographic Pro- 
cess’ following in 1852. His process practically 
displaced both the Daguerreotype and Tal- 
botype (calotype) processes, and enjoyed popu- 
larity from 1855 to 1880. Many historians have 
coupled other names with Archer’s, either as 
assistants or co-inventors, but close study of all 
the facts leads inevitably to the conclusion that 
Archer deserves the whole of the credit. He 
introduced pyrogallic acid (then sold at 6s. 8d. 
per dram) as a developer; a camera within 
which plates could be exposed,.developed, and 
fixed; a triple lens to shorten the focus of a 
double combination lens; and a method of 
whitening collodion positives upon glass (see 
‘‘ Alabaster Process’’). Archer lived and died 
a poor man ; and at his death a subscription list 
was opened and a sum of £747 raised for his 
widow and children. Mrs. Archer died shortly 
afterwards (March, 1858) and the amount was 
settled upon his children, together with a Govern- 
ment pension of £50 per annum. Punch, referring 
to the testimonial, said (June 13, 1857): “To 
the Sons of the Sun.—The inventor of collodion 
has died, leaving his invention unpatented, to en- 
rich thousands, and his family unportioned to the 
battle of life. Now, one expects a photographer 
to be almost as sensitive as the collodion to which 
Mr. Scott Archer helped him. A deposit of 
silver is wanted (gold will do), and certain faces 


Archerotype 


now in the dark chamber will light up wonder- 
fully, with an effect never before equalled in 
photography. . . . Now, answers must not be 
negatives.” 


ARCHEROTYPE, AND’ ARCHOTYPE 


The early names (after Archer, the inventor) 
of the collodion process. 


ARCHITECTURAL PHOTOGRAPHY 


In photographing architectural subjects, 
whether for pictorial or record purposes, regard 
must be paid to the fact that technical correct- 
ness is absolutely essential. Many technical 
points that can be ignored without any serious 
disadvantage in landscapes become important 
in architecture, and disregarding them would 
involve serious loss of quality. The camera 
back must be kept upright so as to secure vertical 
lines in the photograph ; it should be tested with 
a level or a plumb indicator. The one exception 
to this rule is that in many old buildings the 
walls lean outwards, the heavy pressure of the 
roof, acting for centuries, having forced them 
into that position. In that case, the camera 
may be tilted slightly, the back leaning back- 
wards, so as to bring the walls or columns vertical 
in the photograph. Wide-angle lenses, or those 
that include a large expanse of view, become a 
necessity in most architectural work. In exteriors 
as well as interiors, the space is frequently too 
limited to allow a distant point of view to be 
taken, and a lens that will include sufficient of 
the subject from a very short distance becomes 
necessary. Although this is by some regarded as 
a disadvantage, it cannot in every respect be so 
considered. Photographing a subject from a near 
point of view possesses one distinct advantage. 
It conveys the impression of looking upwards in 
a manner that cannot be attained by any other 
means; and this frequently adds impressiveness 
to the picture. Small portions or details can be 
effectively taken with a lens that would be suit- 
able for general landscape work, but larger sub- 
jects require the shorter focus instrument. The 
most useful wide-angle lens will have its focus 
about four-fifths of the longer side of the plate ; 
and if the worker has a second lens, its focus 
should be about the same as the longer side of 
the plate. And the ordinary landscape lens— 
one and one-third the length of the plate—will 
be useful for those subjects that provide suff- 
cient space. The lens, whatever may be its 
focus, should be capable of covering a much 
larger area than the plate in use. In many sub- 
jects the lens has to be raised considerably above 
the centre of the plate, and, unless the lens will 
cover when it is so raised, dark empty corners 
will appear on the negative. Tilting the camera 
to accommodate a lens of limited covering 
capacity is very undesirable ; the front and back 
not being parallel necessitates the use of a very 
small stop to secure sharp definition. 

The camera should be simple and rigid, so 
that long exposures may be given without any 
risk of vibration. The rising front should allow 
the lens to be raised well above the centre; 
almost as far as the top edge of the plate is 
occasionally required. Within reasonable limits, 
the greater the rise obtainable, and the greater 
the covering power of the lens, the more useful 


38 


Argentometer 


and adaptable will be the apparatus for archi- 
tectural subjects. Am anastigmat possesses so 
many advantages that no other type of lens 
should be employed. 

In all subjects an oblique position rather than 
a full front view should be chosen. The latter 
destroys the effect of relief, whereas the former 
shows it effectively. It is very rare that a full 
front view of any subject is effective; the result 
is almost always flat and lacking in interest, as 
the projection of one part of a subject beyond 
another is lost in the picture. A wide-angle 
lens is frequently valuable in enabling the photo- 
grapher to select a more oblique position than 
would otherwise be obtainable. 

A liberal proportion of foreground should 
always be included in front of the nearest import- 
ant vertical object; it assists in conveying the 
impression of space. The normal height of 
vision—s ft. from the ground—is the best for 
all large or high subjects; it conveys the most 
natural impression of size. Photographing from 
a height dwarfs the effect of the building, and 
should be adopted only for special purposes. At 
times the camera may be much lower than 5 it., 
especially for small subjects taken with a wide- 
angle lens. (See “‘ Interiors, Photographing.”’) 

Symmetry in the arrangement of the subject 
on the plate should be studiously avoided ; and, 
equally, an arch, a column, or a doorway that 
may form an important part of the subject 
should never be shown almost but not quite 
completed, broken by the boundary line of the 
picture. It conveys the sense of incompleteness 
and absence of support. Sunlight is very effec- 
tive in some exterior work, especially in compre- 
hensive views of large buildings. In smaller 
subjects, too, it is frequently a valuable aid to 
picturesque quality. At times, the sun shining 
almost along the principal face of the building 
photographed will produce exceptionally good 
effect by throwing very long shadows of all pro- 
jecting details. In many small details, direct 
sunshine is best avoided in order to show the 
form and surface of the details free from cast 
shadows. When photographing in sunshine a 
full exposure is absolutely necessary in order to 
secure transparency and full detail in the 
shadows. (See also “Interiors, Photographing ” 
and ‘“‘ Exteriors, Photographing.”’) 


AREA SYSTEM OF STOPS 

An obsolete system of marking lenses and 
stops suggested in 1886 by George Smith. Every 
stop and every lens had its own number, and 
the relation of the stop number to the lens 
number was supposed to indicate the correct 
exposure. 


ARGENTIC SALTS, OPALS, ETC. 

Argentic salts are salts of silver; argentic 
opals are opals sensitised with silver. Argentum 
is the Latin name, and Argent the French name 
for silver. Sensitised materials of one particular 
make are called argentic opals, paper, etc., but 
bromide opals, paper, etc., are more popular 
names. 


ARGENTOMETER (Fr., Argentométre, Pése 
Nitrate ; Ger., Argentometer, Silbermesser) 


This instrument is used by wet collodion 


Argentotype 


workers for testing the strength of the silver 
bath. It consists of a hydrometer which is 
floated in a tall glass jar. The hydrometer is 
graduated either to show grains per ounce of 
water, parts in a certain volume of water, or 
percentages. The first-mentioned is most 


pene St OO ee 


Peete co ees ee t+e + ere 


ee etree BS eesee 


stores 


Yerces ,eree rer eearvr Os eeosesewee sever ees eererees 


‘ 


- 
i 
‘ 

‘ 

‘ 

' 

‘ 
‘ 
ey 


. 
- 
- - 
= 
= - 
la tt 


Argentometer 


commonly employed by English workers, and 
the second or third by Continental workers. 
The reading is only accurate in case of a new 
bath, as by use the bath becomes charged with 
iodising salts and alcohol from the collodionised 
plates, but for all practical purposes it forms a 
sufficient test. 


ARGENTOTYPE 
A name for bromide paper, and widely used 
in the early days of the bromide process. 


ARISTOGEN 

A concentrated one-solution hydroquinone 
developer, introduced by Liesegang, consisting 
of hydroquinone, sodium acetate, sodium sul- 
phite, and citric acid, for developing faintly 
printed-out gelatino-chloride and collodio-chlor- 
ide papers. According to Schnauss a similar 
and suitable formula is :— 


Hydroquinone (7 °/, alcoholic 


solution) : ‘ HP 4 parts 
Sodium acetate (15 °/, solution) 8 ,, 
Water . : : ; a PRY tg 
ARISTOSTIGMAT (See “ Lens.’) 
ARISTOTYPE 


A gelatino-chloride P.O.P. The original aris- 
‘ totype paper was simply a paper prepared with 
a substratum of barium, and coated with a 
collodio-chloride of silver emulsion, and the 
term was first used early in the ’eighties, Ober- 
netter, of Munich, being the first to introduce it. 
The name is still used by some makers of P.O.P., 
both gelatino- and collodio-chloride, especially 
in America, 
AROMATIC CARBON COMPOUNDS 

A very large class of chemical compounds 


which are derivatives of benzene or contain what 
is known as a closed chain or nucleus similar 


oo 


Artificial Light 


to benzene. Generally, they contain a larger 
percentage of carbon than the fatty or aliphatic 
compounds, and are more frequently crystalline 
at ordinary temperatures, and more easily 
converted into substitution products, especially 
by the action of nitric and sulphuric acids, 
which produce nitro and sulphonic derivatives. 
Most of the newer developers belong to this 
class, 


ARROWROOT (Fr., Arvowroot; Ger., Pfeil- 
wurzelmehl) 

A prepared pure starch obtained from vari- 
ous plants, the finest being the West Indian, 
of which the source is the rhizomes of Maranta 
arundinacea. English arrowroot is the starch 
obtained from potatoes. Arrowroot is used for 
sizing papers before sensitising and also as a 
mountant. 


ARTIFICIAL IVORYTYPES 

Photographs made in 1857, by Mayall, on a 
paper substitute prepared by mixing barium 
sulphate with albumen, and rolling the paste 
into sheets. These, when dry, were printed upon 
and used as paper. 


ARTIFICIAL LIGHT 

Thanks in no small measure to the introduction 
of rapid plates, and of lenses working at very 
large apertures, artificial light has become of 
inestimable service in photography. It is used 
for lighting the subject, for illuminating the dark- 
room, and for printing. The actinic power is 
obviously important, and the following table 
gives the approximate comparative powers of 
the illuminants in common use, a standard candle 
being taken as I :— 


ACTINIC POWERS OF ARTIFICIAL LIGHTS 
Standard candle 


Colza lamp, 4-in. wick 2 
Paraffin lamp, 4-in. wick . 4 

rE » I-in. wick . IO 
Paraffin duplex lamp 30 
2-ft. gas burner 12 
5-it. ” ” i : . 35 
16-c.p. electric incandescent lamp 35 
32-C.p. ” ” 7O 
Welsbach incandescent gas 80 


Sir William Abney gives the following table, 
showing the photographic value of some artificial 
lights in terms of the photographic value of a 
standard candle, the photographic value being 
taken as the effect on bromide of silver :-— 
Light of the Optical Value Photographic Value in 

of one Standard Candle Terms of Standard Candle 

Standard candle ; , I 
Ordinary paraffin candle 


; ofa 
Oxyhydrogen light, blow-through 
seb : ‘ : a ae 
Electric arc light. ‘ Powe fe) 
Magnesium burnt at the rate of 
I gr. per minute. rae 3. 
Bright sun at noon in summer 21°6 


Referring to the above, Sir William Abney says: 
“Tt will be noticed how the optical and photo- 
graphic values differ. It might be thought that, 
although these differences do exist, yet, by 
increasing the smaller number, the same effect 


Artificial Light 


might be obtained. It must be recollected, how- 
ever, that the electric light radiates from 1,000 
to 10,000 candles from a very small area, and 
that, to make the same photographic illumin- 
ation, the number of candles would have to be 
the same, but multiplied by 10. Thus, if an 
electric arc light radiated 1,000 candles, the 
number of standard candles that would have to 
be employed would be 10,000, a number which 
would never be concentrated in any reasonable 
area, Sunlight may be taken as equal, optically, 
to 5,600 candles placed at one foot from the 
object illuminated.” 

The electric arc and the mercury vapour lamps 
ate the most powerful for photographic purposes, 
and largely used by professional workers because 
of their richness in those rays to which dry plates 
are the most sensitive. The light from incan- 
descent electric lamps is usually of a yellowish 
tint, serviceable enough for printing, dark-room 
illumination, etc., but hardly strong enough for 
portrait work unless used in large numbers. 
Acetylene gives a very serviceable and intensely 
actinic light for most photographic purposes. 
The artificial light that is most generally used 
for printing, however, is the incandescent gas 
mantle, which, when of an average quality 
and full size, gives a light of between 60 and 
70 candle power. Magnesium, in the form of 
either powder or ribbon, is extensively used for 
portrait work outside the studio at night, its 
use dating from 1863. Ribbon and powder, 
weight for weight, give approximately the same 
illumination ; and one inch of ribbon in contact 
printing is equal to four minutes’ exposure to 
an ordinary flat flame gas burner at the same 
distance (see also ‘‘ Flashlight Photography ’’). 
In 1882 a lamp was devised for burning magne- 
sium ribbon in oxygen; a number of improve- 
ments followed, and the lamp is now an article 
of commerce. Ordinary gas burners, oil lamps, 
and candles give lights that are of poor actinic 
value. As regards the cost of some illuminants, 
eon Gaster, A.M.I.E.E., has given the following 
table :— 

Cost per 1,000 
hours per candle 


power. 
Petroleum “ ; 908d. 
Alcohol incandescent seers. 
Auer burner, incandescent gas . 3°17. 
Pressure gaslight, incandescent. 2-12d. 
Carbon filament lamp ae y hs eae lt 
Nernst lamp . . shy etoeine 
Arc lamp. ; . en EEO 
Flame arc lamp . oi) 4, L006, 
(See also ‘* Acetylene,” ‘* Flashlight Photo- 
graphy,” ‘‘Candle Power,” “Limelight,” 


** Artificial Light, Portraiture by,” etc.) 
ARTIFICIAL LIGHT, PHOTOGRAPHY 
BY 


Photography by artificial light presents no 
serious difficulty if proper precautions are taken, 
and a correct exposure given. It is imperative 
that the source of light should be in such a 
position that no direct rays reach thelens. When 
it is unavoidable that the source of light is in 
front of the camera, the lens may have fitted to 
it a sky-shade or a large temporary hood, so 


40 


Artificial Light 


as to protect it from the light. Whenever pos- 
sible, the source of light should be behind the 
camera, not directly at the back, but at one side 
or the other. Where the arrangement of the 
light is under the photographer’s control, and 
the light is of such a nature that it can be divided, 
the larger part should be placed at one side and 
behind the camera, and the smaller part at the 
other side. Even where the light is fixed, but 
divided, as with two or more electric arc lamps, 
a similar result may be obtained by placing the 
camera so that one light is almost directly 
behind it, slightly to one side, and the other one 
considerably towards the other side. When 
practicable, the light should be diffused by a 
screen of tissue paper. This softens the light, 
and destroys the harshness of the cast shadows, 
which would otherwise be very strongly marked. 

When photographing an interior, or a small 
object in a building, by electric arc lamps, the 
strength or actinic value of the light may be 
tested by means of an actinometer while the 
camera and subject are being arranged. For 
a room about 4o ft. by 25 ft. or 30 ft., with the 
camera and a single are light of about 2,000 
candle power at one end, the exposure should be 
ten minutes, using a lens aperture of f/16 and a 
plate of a speed of 200 or 250 H. & D. Fora 
small object photographed at a distance of 6 ft. 
or 7 ft., illuminated by a single arc light of 
2,000 candle power at a distance of 10 ft. or 
12 ft., the exposure should be five or six minutes 
for a light-coloured object, up to twelve or fifteen 
minutes for one of dark colour. 

Where arc lamps are not available, magnesium 
ribbon or powder, or a mixture of magnesium 
and aluminium, may be employed. The powder 
is frequently burned in the form of a flash, and 
though this may be desirable when groups of 
persons have to be included, the methods in 
which the powder is burned more slowly are 
preferable. Magnesium alone produces consider- 
able smoke in burning, and though this smoke 
is only in evidence after the exposure is com- 
pleted, it is a serious objection in many cases, 
and quite prohibits making a second exposure, 
(See “‘ Flashlight Powders.’’) 

A convenient form of artificial light easily 
obtainable is that sold under the name of 
**Flash Candle.’”’ These candles consist of a 
celluloid tube filled with a perfectly safe mixture 
which burns for a few seconds and produces a 
light of great intensity. They are obtainable in 
various sizes, called two-second, four-second, and 
seven-second candles respectively. Two, three, 
or four of these may be placed in suitable posi- 
tions for lighting an interior, and they may be 
lighted in rapid succession by applying a lighted 
taper to the touch-paper with which each candle 
is provided. Focusing and arranging must be 
done before lighting the candles. A room or 
space about 25 it. by 16 ft. would be sufficiently 
illuminated if the camera and lights were at one 
end and two four-second candles were burned, 
using alens aperture of f/16 anda plate having a 
speed of 200 or 250 H. & D. As in the expo- 
sures given for electric light, it is assumed that 
there is a wall near the lights, or an equally 
well-lighted space beyond. If these candles 
or an electric light were used to illuminate a 
small space which formed part of a large room 


Artificial Negatives 


or open space, in such a manner that there was 
a large open dark space beyond the light, at 
least half the illumination would be lost by 
diffusion, 

Still life and flower photography may be 
carried out very successfully by artificial light, 
using either magnesium ribbon or the flash 
candles. One four-second candle at a distance 
of 3 ft. should be sufficient, using the lens at f/16 
and a 200 H. & D. plate; a screen of ground 
glass or tissue paper for diffusing the light is 
imperative, and a white reflector behind it. 

Copying may be done in a similar manner, or 
by means of the ordinary gas or electric house 
lighting. Two lights should be used if possible, 
one placed at each side of the camera, so as to 
light the work to be copied as evenly as possible ; 
or half the exposure may be made with a single 
light at one side, and then the light placed at 
the other side for the remainder of the time. 
When copying a print with a glossy surface, care 
must be taken to avoid the sheen that may be 
produced by an improperly placed light. For 
copying a photographic print, the same size as 
the original, using a 50 candle-power gas or 
electric light placed about 2 ft. from the print, 
the exposure required for f/16 and a plate 200 
H. & D. would be about five minutes. For 
copying a black print on plain white paper—a 
line engraving, for example—two minutes would 
be sufficient. 

For rapid work by artificial light, see under 
the headings “‘ Flashlight Photography” and 
“‘ Flashlight Powders.”’ For the application of 
artificial light in the production of prints, see 
under the headings “Bromide Paper” and 
“Gaslight Papers and Lantern Slides.” 


ARTIFICIAL NEGATIVES 

Hand-made, and not photographic negatives ; 
known also as factitious negatives. An opaque 
ground or varnish is spread on glass, and, when 
dry, is scratched through with a needle point, 
making a drawing after the style of an etching. 
The process is also used for making lantern slides 
(positives) of diagrams, writing, etc. Asphalt 
varnish to which wax is added until a pliable 
ground is obtained makes a suitable coating. 
If the ground is sticky or is not dense enough it 
may be dusted over and polished with fine 
blacklead, such as is used by electrotypers. 
White grounds may also be formed by dusting 
with blanc d argent. A wet plate may be fogged, 
developed, and intensified to form a ground; 
and there are numerous other methods of pre- 
paring such plates, 


ARTIGUE PROCESS 

A modification of the carbon process, named 
after its inventor, Mons. Artigue. No safe- 
edge is necessary on the negative, there is no 
transfer, and consequently the print is not 
reversed. The paper for this process is sup- 
plied coated with a mixture of a colloid sub- 
stance and a very fine black pigment. It is 
supplied insensitive, and requires to be sensi- 
tised by floating on a 2 per cent. solution of 
potassium bichromate. A thin negative is most 
suitable for this process, and the exposure of 
the print is timed by means of an actinometer 
as in ordinary carbon printing. An essential 


41 


Artograph 


feature of the process is the method of develop- 
ment. A very fine sawdust is supplied by the 
makers of the paper; this has to be mixed with 
water to about the consistency of a thick soup. 
The print is soaked in tepid water for a few 
minutes, and then laid face upwards on a sheet 
of glass. The sawdust and water mixture, 
preferably tepid, is poured over the print from 
a jug. The print is rinsed from time to time so 
that the progress of development may be judged, 
and the pouring of the sawdust mixture is con- 
tinued until the print is sufficiently light, exactly 
as the pouring of water in an ordinary carbon 
print. As soon as development is completed, 
the print is well rinsed to remove any of the 
sawdust that may adhere, then placed in a 
5 per cent. solution of alum for five minutes, 
tinsed in two or three changes of water, and 
dried. The surface of the prints is exceedingly 
delicate, and very great care has to be exercised 
throughout to prevent injury. The prints pro- 
duced by this process are characterised by very 
great delicacy and rich quality. They have a 
delicate velvety matt surface, the deepest 
shadows are a rich black with full detail, and 
the scale of gradation is good. 

The Artigue process has never been exten- 
sively worked in England. Suggested reasons 
are the extreme tenderness and delicacy of the 
coating, which necessitates great care at all 
stages, and the difficulty experienced in obtain- 
ing the materials. The introduction of the gum- 
bichromate process has lessened the demand for 
a paper of the Artigue character, and several 
attempts to introduce a paper somewhat similar 
have met with very slight success. It must be 
conceded, however, that none of the substitutes 
has equalled Mons. Artigue’s production in 
delicacy of surface, in richness of quality, or in 
gradation. 


ARTISTIC PHOTOGRAPHY 

A frequently used but somewhat vague term. 
The idea underlying it is that the producer of a 
given picture has aimed at something more than 
a merely realistic rendering of the subject, and 
has attempted to convey a personal impression. 
Thus, a landscape may be rendered solely as a 
topographical view or as the material for con- 
veying the idea of, for example, solitude; an 
interior may be intended to show architectural 
detail or to suggest, for example, grandeur The 
results are consequently either realistic or 
attistic. The artistic element becomes more 
pronounced the more the merely mechanical 
and thoughtless is subordinated to the deliber- 
ate and intentional control of the producer. 


ARTOGRAPH 

An automatic machine, known also as the 
electric artograph and telautograph, for sending 
sketches or line drawings along a telegraph wire, 
invented about 1891 by N. S. Amstutz, of Cleve- 
land, Ohio. According to a description published 
at the time, the picture was photographed on a 
“stripping film” of gelatine and potassium 
bichromate, which, after washing with luke-warm 
water to remove the portions not hardened by 
the action of the light, gave a picture in relief, 
more or less high, according to the tones of the 
original, The next step was to vary the strength 


Artotype 


of current in the telegraph wire according to the 
variations of light and shade in the picture— 
that is to say, according to the heights and depths 
of the etched film. This was done by an arrange- 
ment similar to the stylus which moves over the 
indentations on the wax surface of the phono- 
graph. ‘The point of the stylus passed over every 
part of the film, and tripped up and down accord- 
ing to the degree of relief. By a multiplying 
lever its movements up and down were caused 
to depress a series of keys which completed the 
electric circuit. If the relief was very low only 
one key was depressed, and more keys were 
closed in proportion to the depth of the relief. 
The current was thus varied in strength accord- 
ing to the degree of relief on the film. At the 
receiving end the current passed through an 
electromagnet, which bore with more or less force 
on a travelling graver, according to the strength 
of the current, and the design was cut in a surface 
of’ wax, from which an electrotype could be 
obtained for printing purposes. The results 
published at the time of the introduction of the 
system were crude. 


ARTOTYPE 

A name give to an early collotype process in 
which the plate was given two separate coatings 
of bichromated gelatine instead of, as at present, 
one. 


ASKAU PIGMENT PRINTING PROCESS 
(Fr., Procédé Askau ; Ger., Askau-Druck) 
A dusting-on process introduced in Germany 
by Joseph Rieder, in 1909, in which pure india- 
rubber (caoutchouc), with a small proportion of 
asphalt added, is used as the sensitising material. 
Paper coated with the mixture will keep for a 
month. It is exposed under a positive trans- 
parency, as in other dusting-on processes, and 
is “‘ developed’ with a mixture of sea-sand and 
a suitable powdered pigment, the latter adhering 
to the light-affected parts according to the 
exposure each portion has received. A lac 
varnish is then sprayed over the print by means 
of an air brush to fix the pigment. 


ASPHALT 


The chief of the many synonyms for asphaltum 
(which see). 


ASPHALT PROCESS 


A ptocess of using asphaltum for photo- 
etching. (See “ Asphaltum.”’) 


ASPHALTO-PHOTO-LITHOGRAPHIC PRO- 
CESS (Fr., La Photolithographie au 
Bitume ; Ger., Asphalt-Photolithographie) 

An adaptation of the bitumen process of 
Joseph Nicéphore Niepce. A lithographic stone 
is coated with a solution of bitumen in ether, or 
other suitable solvent, and is exposed to light 
under a negative. The light-affected parts are 
rendered insoluble, and the unexposed portions 
may then be dissolved away by the application 
of ether, After rinsing and allowing to dry, the 
stone is wetted with gum water, which is applied 
with a sponge. When dry, the surface gum is 
washed off with a slightly-damp cloth and the 
stone is lightly etched with a very weak solution 
of nitric acid. It is then rinsed to remove the 


42 Asphaltum 


acid, again gummed, and, when dry, wiped with 
the damp cloth, after which it is ready for print- 
ing from in the ordinary lithographic manner, 
wetting the stone at each impression. The same 
process can be employed with zinc or aluminium 
plates. (See also “* Photo-lithography.”) 


ASPHALTOTYPE 

A name given to one of the processes for using 
light sensitive asphalt for making typographic 
printing blocks. (See also “ Asphaltum.’’) 


ASPHALTUM (Fr., Asphalte, Bitume de Judée ; 
Ger., Asphalt, Judenpech) 

Synonyms, asphalt, bitumen, bitumen of 
Judea, mineral pitch, and Jew’s pitch. A 
natural product of the decomposition of vege- 
table substances. 

The term asphaltum comes from the Greek 
word for fossil pitch, jacpadros (and cparAopmat) 
and signifies an unchangeable body. The 
Latin word bitumen is derived from prx tumens. 
Geologically, asphalt is, as stated above, a 
natural product of the decomposition of vege- 
table substances; and it is found in all parts 
of the world, most frequently in volcanic neigh- 
bourhoods. The principal sources are on the 
shores of the Dead Sea in Syria (whence comes 
the name Syrian asphaltum), and in the Great 
Pitch Lake of the Island of Trinidad; but it is 
also found in the Lake of Maracaibo (in Vene- 
zuela), at Coxitambo (in Peru), at Barbadoes, 
and in the island of Cuba; whilst in Europe 
there are deposits at Seyssel and at Bechel- 
bronn (in Alsace). Small deposits have been 
found in Cornwall, Derbyshire, and Shropshire. 
For photographic processes, however, only the 
Syrian and the Trinidad asphaltum are con- 
sidered, these having the characteristic pro- 
perties of asphaltum—namely, brownish-black 
colour, high melting point, and conchoidal frac- 
ture. Bitumen has usually been considered to 
be formed by the oxidation of petroleum, and 
according to the generally accepted analysis is 
composed of carbon, hydrogen and oxygen, with 
a small quantity of nitrogen, together with 
sulphur and mineral substances (iron, man- 
ganese and calcium). Syrian asphalt comes into 
the market in large pieces, which frequently con- 
tain small lumps of earthy substances consisting 
of carbonate of lime, gypsum, clay, and sand. 
Trinidad asphalt also comes into commerce in 
large pieces, which, however, do not contain 
the earthy particles found in the Syrian. The 
commercial asphalt can be purified by boiling in 
water, when the pure asphalt melts and floats 
upon the surface while the impurities subside. 
The Syrian asphalt begins to melt at 275° F. 
(135° C.), and the Trinidad at 266° F. (130° C.). 
The specific gravity of the former is 1-103, and of 
the latter 1°96; both kinds behave the same in 
relation to solvents. They are partly soluble 
in alcohol and ether, more so in benzole, com- 
pletely and easily soluble in chloroform, bisul- 
phide of carbon, tetrachloride of carbon, tur-. 
pentine and the various mineral oils. They are 
insoluble in solutions of caustic potash or soda, 
weak or strong, hot or cold. With concentrated 
sulphuric acid the Syrian asphaltum is decom- 
posed, but only by the heat, with evolution of 
sulphurous acid, and it dissolves into a dirty 


Asphaltum 


brown flvid. Concentrated nitric acid has but 
very little action on it, even with heat. 

The results of analysis show that the Syrian 
and Trinidad varieties are similar in com- 
position. Each is found to contain Io per cent. 
of sulphur, and this constitutes an important 
factor in regard to photographic sensitiveness. 
By successive treatment with boiling alcohol, 
boiling ether and chloroform, it is found that 
both kinds may be separated into three com- 
ponents, differing in their chemical composition 
and photographic properties. The portion (a) 
insoluble in ether shows the highest sensitive- 
ness, (b) the substance soluble in ether is less 
sensitive, and (c) an oily substance extracted by 
alcohol is quite insensitive. The part that is 
insoluble in ether is, as a rule, easily soluble in 
chloroform and turpentine, and less so in benzole 
and petroleum. Syrian asphaltum contains 
52 per cent. of the sensitive component, while 
Trinidad contains only 38 per cent. 

Spectroscopically examined, solutions of Syrian 
asphaltum of the most sensitive kinds show weak 
absorption bands, whilst the less sensitive kinds 
show the bands more strongly. 

As obtained from dealers, asphaltum is gener- 
ally fit to be used at once; but, if necessary, it 
may be purified by powdering it and digesting 
it with dilute hydrochloric acid, which dissolves 
the earthy particles. Some authorities recom- 
mend a treatment with boiling water, by which 
soluble and earthy particles may be separated 
out. In order to obtain the most rapid results, 
it is desirable to extract the least sensitive con- 
stituent of the asphaltum with ether, and use 
the residue in making the sensitive solution. 
The simplest way of doing this is to digest the 
powdered asphaltum in a bottle with an excess 
of ether, shaking it up from time to time, and, 
if necessary, stirring it with a glass or wooden 
rod. The ether is changed at intervals of a few 
hours, till all or nearly all the soluble constituents 
are removed. ‘The last ether is then poured off, 
and the residue thoroughly dried. Husnik’s 
asphaltum, which is believed to be prepared in 
some such way, is obtainable as an article of 
commerce in the dry powder form. The solvent 
used for making up the sensitive solution is 
generally benzole, which should be quite free 
from water. Sometimes chloroform is added, 
and generally some essential oil, such as lavender 
or lemon, which prevents the too rapid drying 
of the coating, and so keeps it uniform; the 
addition of oil is said to increase sensitiveness. 

The following is a practical formula for pre- 
paring a sensitive solution of asphaltum for 
coating zinc plates for etching : Dissolve 150 grs. 
of finest powdered Syrian asphaltum in 2 oz. 
of chloroform and 3 oz. of anhydrous benzole. 
Add 30 grs. of Venice turpentine and 10 drops of 
vil of lemon or oil of lavender. The film should 
be of a transparent golden yellow tint. The 
coating should be done by means of a whirler 
(which see). ‘The exposure is best made under 
stripped films, which may be treated with a 
bath of glycerine to make them adhere when 
squeegeed down to the plates. It is not necessary 
to use a printing frame. The exposure may vary 
from half an hour in the sun to two or three 
hours in the shade. In bad weather the exposure 
may extend to days. Development is usually 


43 


Aspirator 


done with turpentine, which dissolves the soluble 
parts of the image. The scum is rinsed away, 
and the greasiness removed from the surface 
with soap and water or a weak solution of soda. , 

Prof. Valenta has published a process for 
augmenting the sensitiveness of bitumen by 
incorporating sulphur with it. By this process, 
100 g. (3% OZ. II grs.) of raw Syrian asphalt 
are boiled in a retort with an equal quantity 
of raw pseudo-cumene—which has the formula 
C3H;(CH,)., and a boiling point of about 170° C.— 
and 12 g. (186 grs.) of flowers of sulphur 
which should have been previously dissolved in 
the pseudo-cumene. When after about three or 
four hours’ boiling, the evolution of sulphuretted 
hydrogen has ceased, the pseudo-cumene is dis- 
tilled off and the black pitchy residue dissolved 
in benzole in the proportion of 4 to 100, which 
solution is used for the sensitive coating of the 
plate or stone. The sulphurised asphalt pre- 
pared in this way is almost insoluble in ether, 
but dissolves fairly readily in benzole, toluene, 
xylene, cumene, and turpentine, and is very 
sensitive to light. Recently Prof. Valenta has 
simplified his method by dissolving the asphaltum 
in carbon disulphide and adding sulphur chloride. 

A number of processes mostly used for photo- 
lithography take advantage of the fact that 
when bitumen is dissolved in both alcohol and 
ether in suitable proportions it will split up into 
a grain on drying. ‘The film can then be printed 
under an ordinary continuous tone negative and 
yield a picture in half-tones. The Frey process 
is a successful method worked on this basis. 

Bitumen processes are not much employed 
nowadays, owing to the slowness and uncertainty 
of the exposures. Bitumen powder is, however, 
largely used for dusting on plates to strengthen 
the resist for etching, and the solution is used as 
a resist varnish for the backs and margins of 
plates, and for stopping out. 

Alberini’s reversed bitumen process consists 
in removing the exposed bitumen from, the 
metal plate instead of the unexposed bitumen as 
in the ordinary process. This makes it possible 
to expose the bitumenised zinc plate under an 
engraving, print, or inked drawing on thin 
paper, dispensing with the use of a negative. The 
preparation of the plate and exposure follow 
on the lines of the ordinary process, but develop- 
ment is effected by immersing the plate in a 
dish of 40 per cent. alcohol. The principle of 
the process is that the alcohol dissolves the part 
which has been acted on by light, and not the 
unexposed part, which is usually developed with 
turpentine. 


ASPIRATOR 

An instrument used to promote the flow of 
gas or liquid from one vessel to another by 
suction. In its simplest form it is a cylindrical 
glass or other vessel having a pipe to admit air 
at the top and a stop-cock at the lower end. 
A shows a simple form of aspirator bottle. Asa 
container for solutions which must be kept in 
bulk free from air, it is shown at B. The large 
bottle c contains, say, a hydroquinone-metol 
developer and has two glass tubes, one of which 
F reaches to the bottom; F passes through a 
rubber stopper and is continued down below the 
shelf, having a piece of rubber tubing with a 


Aspray-Fisher 


clip and a piece of drawn-out tube at the end. 
The other tube E just pierces the rubber stopper, 
and is connected with a small bottle p containing 
about 50 grs. of pyro dissolved in 2 oz. of a 
10 per cent. solution of caustic soda. The 
tube from the large bottle just pierces the rubber 
stopper in the smaller one, while a third tube c 
goes to the bottom, its other end being open to 
the air. This tube should be high enough to 
prevent the pyro-soda mixture being forced out 
of the bottle. To use the arrangement, unclip 
the rubber at the end of the tube F and blow 
through G. This forces the developer up and 
down the tube F and so creates a siphon, it 
being then only necessary to unclip the tube to 
obtain developer from the large bottle down the 
tube. The solution in the small bottle filters 
the air from both carbonic acid and oxygen, 
and the developer keeps good indefinitely. If 


A. Aspirator 
Bottle 


B. Aspirator for Solutions 
to be kept from Contact 
with Air 


the depth of the liquid in the small bottle exceeds 
3 inches, the tube F should be at least 6 inches 
below the shelf. 


ASPRAY-FISHER ANIMATED STEREO. 
GRAMS (Fr., Méthode Aspray-Fisher de 
la Stéréoscopie Animée; Ger., Aspray- 
Fisher Lebendige-Stereographie) 

An invention patented in 1859 by C. Aspray 
and R. Fisher. The two halves of a pair or 
series of stereoscopic pictures are so taken as 
to be views of the same person or object in 
slightly different positions. By rapidly opening 
and closing each eyepiece in turn with a revolving 
disc, so that either eye is alternately eclipsed, 
the illusion of motion combined with stereo- 
scopic relief is obtained. This is the earliest 
recorded attempt to combine apparent movement 
with the effect of natural relief and modelling. 


ASTIGMATIC CORRECTOR 


A negative attachment for removing the 
astigmatism of portrait lenses. It was invented 
by T. R. Dallmeyer in 1897. Although highly 
successful in producing a perfectly flat and non- 
astigmatic field, the corrector was never placed 
upon the market, as it was found necessary to 
grind special glasses for each individual lens. 
The focal length of the portrait lens was increased 
by from 30 to 40 per cent. with, of course, a 
corresponding decrease in rapidity. 


44 


Astrophotometry 


ASTIGMATION 


An old and practically obsolete synonym of 
astigmatism. 


ASTIGMATISM 


A serious defect in many lenses by which they 
are prevented from rendering vertical and hori- 
zontal lines with equal degrees of sharpness. It 
is more noticeable towards the edges of the field, 
the centre being quite free from it. The defect 
is best explained by a diagram. If, using a lens 
defective in this way, a clearly defined cross is 
focused in the centre of the field, it will go 
evenly out of focus on moving the screen to and 
fro, the edges being uniformly blurred as at A. 
Upon focussing the same cross near the margin 
of the plate, the vertical or horizontal line only 
will be blurred, the other becoming sharper as 
the screen moves to one side or the other of the 


IN 


ew 


IE 


A 
TT (a 
.. S 


Blurred Images due to Astigmatism 


focal plane of the image, as at B. In like 
manner, a circle is drawn out into an ellipse 
either horizontally or vertically, as the case 
may be. Astigmatism may be minimised by 
the employment of a small aperture, but cannot 
be entirely removed. It is usually found in 
portrait and rectilinear lenses, and may be partly 
cured by shortening the tube; this, however, 
has the disadvantage of increasing the curvature 
of field. . 


ASTRO - PHOTOGRAPHY. | (See “ Stars, 
Photographing,” ‘Celestial Photogra- 
phy,’ ‘Comets, Photographing,” etc.) 


ASTROPHOTOMETRY 


The use of the photographic plate for astro- 
photometry is not unattended with disadvan- 
tages, for whilst the correction of the instruments 
may be good it is impossible to bring all the rays 
to an accurate focus, and they are grouped in 
rings around the actual image of the star. As 
the brightness of the star increases, or the expo- 
sure is prolonged, the image not only becomes 
denser, but also widens; therefore it has been 
suggested to estimate the magnitude of the star 
both by the density and the increase in diameter, 
or either. Unfortunately, the law breaks down 
that increase of the exposure is equivalent to the 
increasing of actinic luminosity, but it has been 
found to apply to stars down to the eleventh 


Atmography 


magnitude. When the diameter of the star 
image is used, an allowance has to be made for 
the duration of exposure, and this has to be 
determined for every plate and instrument, but 
may then be taken as constant. When the 
density of the image alone is used, Pickering and 
Schwarzschild independently suggested that the 
out-of-focus images should be photographed 
when they no longer appreciably differ in size 
but do in density. One of the chief difficulties 
to which attention has only been recently directed 
is the effect of the different colours of the stars, 
for obviously a blue star and a red star photo- 
graphed on an ordinary plate and then on a 
panchromatic or red-sensitive plate would 
present totally different images, not only as 
regards size, but density. 


ATMOGRAPHY 

The name given to the curious effects on sensi- 
tive plates and papers caused by emanations and 
vapours from sugar, eggs, smoke, and other sub- 
stances, sometimes referred to as effluviography 
and vapography. 


ATMOMETER (Fr., Atmométre ; Ger., Dunst- 
messer ) 
An instrument for measuring the quantity of 
water passing into the air by evaporation in a 
given time. 


ATMOSPHERE, RENDERING 

In the pictorial sense the word atmosphere 
is generally used to indicate a certain amount 
of visible vapour or mistin the air. The presence 
of mist is frequently a valuable aid to picture 
making, often imparting a suggestion of delicacy 
and mystery to subjects that are less satisfactory 
when the air is clear and the light bright. The 
rendering of subjects under these conditions is 
not alwayseasy. The exposure must be carefully 
timed, and development must be so adjusted 
as to secure a negative of soft and delicate 
gradation. ‘The use of a colour screen, or light 
filter, is generally a disadvantage, as it has a 
tendency in certain conditions to make the 
veiled distance clearer and brighter than it 
appears. The best result is obtained with a 
full exposure on an ordinary plate, followed by 
development carried only far enough to secure 
detail and gradation without blocking up the 
lighter tones. A delicate grey print in bromide 
or platinum is frequently the best presentment 
of the effect. 


ATMOSPHERIC ACTION 

The atmosphere is a mixture of oxygen and 
nitrogen containing always more or less car- 
bonic acid and aqueous vapour. In the neigh- 
bourhood of cities there is also more or less smoke 
and traces of sulphur compounds, and occasion- 
ally ammonia. All developing agents when 
exposed, either in the solid state or in solution, 
to the air greedily absorb oxygen, and they 
discolour and become less active, the oxidation 
products not being developers. Silver in a 
finely divided state, as it occurs both in nega- 
tives and prints, is extremely liable to be attacked 
by any sulphur compounds, particularly when 
gelatine is the vehicle, as this readily absorbs 
aqueous vapour and thus brings the deleterious 


45 


Aurora Yellow 


sulphur compounds into more intimate contact 
with the silver of the image. 


ATOMIC WEIGHTS (Fr., Poids atomiques ; 
Ger., Atomgewichte) 

A term relating to the number of atoms form- 
ing a molecule of any element, according to the 
atomic theory. On the atomic weights are based 
the molecular or equivalent weights, and a list of 
these is given in a table to be found under the 
heading “‘ Solubilities.”’ 


ATZPINSEL (Ger.) 

A round, mop-shaped brush (see illustration) 
of soft hair, generally marten fur, bound to a 
wooden handle by means of waxed string 
varnished with shellac. It is used for brushing 


Atzpinsel 


the surface of the metal plate in etching, to free 
the image from scum. It is also occasionally 
employed in etching on copper with iron per- 
chloride when the plate etches slowly and there 
appears to be a deposit in the hollows. 


AURAMINE (Fr., Auvamine ; Ger., Auramin) 

Synonyms, auramine yellow, amidotetra- 
methyl diamido-diphenylmethane hydrochloride. 
Solubilities, soluble in water, alcohol, and 
ether. A sulphur-yellow-coloured aniline dye 
which is sometimes used for making light filters 
or yellow screens. It is unsatisfactory in this 
respect, as it passes the bright blue, the extreme 
end of the violet, and ultra-violet, absorbing only 
the deep blue. 


AURANTIA (Fr., Aurantia ; Ger., Aurantia, 
Katsergelb) 

Solubilities, slightly soluble in water, very 
soluble in alcohol. An orange-coloured aniline 
dye used for making light filters. Much superior 
filters can be made with other yellow dyes— 
that is, filters that do not absorb so much red 
and orange as those made with aurantia. 


AUREOLINE (See ‘ Primuline Yellow.’’) 


AURIC CHLORIDE (See “ Gold Chloride.’’) 


AURIN (Fr. and Ger., Aurin) 

Solubilities, insoluble in water, soluble in 
alcohol. A mixture of aurin, methyl-aurin, and 
corallin aniline dyes occurring in yellowish 
brown lumps with greenish fracture. It is 
occasionally used for making coloured spirituous 
backing. 


AURORA YELLOW 

A fine yellow pigment used both as a water 
colour and as an oil colour. It is cadmium 
sulphide CdS, prepared by passing sulphuretted 
hydrogen SH through a solution of cadmium 
chloride CdCl,, the precipitate being washed 
with hot water and dried. A final treatment 


Aurotype 


with carbon disulphide CS, is desirable, as this 
removes free sulphur. 


AUROTYPE (Fr. and Ger., Aurotypie) 

A printing process made known in 1844 by 
Robert Hunt, in which gold chloride was 
used in conjunction with potassium ferricyanide 
and ferrocyanide. Hunt published other print- 
ing processes in which salts of gold were em- 
ployed. 


AUROUS CHLORIDE (See “ Gold Chloride.’’) 


AUTOCHROM, OR AUTOCHROM PRINT- 
ING 

A combination of typographic and litho- 

graphic printing used for cheap colour work, 

such as coloured postcards. The keyplate is a 

half-tone typographic block, and the colours are 

filled in with tint plates printed lithographically. 


AUTOCHROME PROCESS 

A process of screen-plate colour photography 
invented by MM. Lumiére[Eng. Pat. 22,077, 1904; 
28,718, 1904; 9100, 1906], based on the use of 
starch grains, asfar as possible of a uniform size, 
dyed to the necessary colours, red, green and 
blue violet, mixed and sifted on to glass coated 
with a tacky surface. The grains are then rolled 
and any white interspaces filled with a black 
pigment. The screen-plate thus formed is 
coated with a panchromatic emulsion. (See 
‘*Screen-plate Processes.”’) 

The plate is placed in the dark-slide so that 
the glass side faces the lens, and a black, smooth 
card should be placed in contact with the sensi- 
tive emulsion to prevent any damage to the 
latter. A yellow screen must be used to cut 
down the excessive action of the blue violet 
and blue, and the makers provide special screens 
for this purpose, though the following, sug- 
gested by Von Hiibl, has proved satisfactory in 
practice :— 


A. Tartrazine 154 gts. I g. 
Distilled water 174 Oz. 500 ccs 

B. Phenosaffranine 5 ers OF 2 
Distilled water 2440zZ. gooccs 

C. Gelatine 93 gts. 6g. 
Distilled water 3. OZ. 85 ccs 


640 minims or 38 ccs. of C should be mixed 
with 168 minims or 10 ccs. each of A and B. 
Immediately before use, 6:2 grs. or 0-4 g. of 
zsculine dissolved in 338 minims or 20 ccs. of 
water with 3 or 4 drops of ammonia should 
be added to the dyed gelatine; it is important 
to make the esculine solution only just before 
use, as it rapidly discolours. Of this dyed gela- 
tine, 140 minims or 7 ccs. should be coated on 
every 16 Sq. in.or every 100qcm. The exposure 
must be determined by meter, or the speed of 
the plate may be taken as approximately 
2H. & D. or 3 Watkins, but, unfortunately, 
the speed varies practically both in sunlight 
and shade, and in winter and summer, this 
variation being dependent on the spectral com- 
position of the light. 

After exposure the plate should be developed, 
and the developer first recommended was pyro- 
ammonia, but a later recommendation is the 
following :— : 


46 


Autochrome Process 


Quinomet (metoquinone) 62 grs. 4 g. 
Sodium sulphite (anhydrous) 278 ,, sg. Tae 
Liquor ammoniz (-880) 4 mins. 0-2 ccs. 
Potassiuin bromide 154 gts. Rig; 


Distilled water to 35 OZ. 1,000 ccs. 


The duration of development should be 23 
minutes at a temperature of 60° F. (155° C.). 
Many other developers may be used, such as.a 
normal metol-quinol developer or rodinal 1 in 12 
for six minutes, amidol, rytol, etc. 

As the emulsion is very sensitive to red, the 
plates must be worked in total darkness or in a 
deep green light such as is obtained through 
the following filter, and even then the plate 
should be exposed to this light as little as 
possible :— 


New Bordeau R 3 °/, 


solution . 2402. 125 ccs. 
Tartrazine 4 °/, solu- 

tion ; - ; sae 150) %, 
Light green S 5 °%/, 

solution ; [oe :7e" 
Glycerine : : Lees = Bete 
Gelatine 10 °/, solu- 

tion to. <' Oes 1,000 4, 


2 oz. or 56 ccs. should be coated on every 
100 sq. in. or 645 qcem. Or, in place of the 
above, fixed-out dry plates may be dyed in 
tartrazine and methyl violet to form a red 
screen, which should be placed in contact with 
one stained with malachite green, and if a brilliant 
light is used a sheet of tissue paper, stained with 
tartrazine or malachite green, should be placed 
between them. 

At the conclusion of development the plate 
should be rinsed for fifteen to twenty seconds, 
and then immersed in the following reversing 
bath :— 


Potassium permanganate 31 grs. eA 
Sulphuric acid . 170 mins. I0 ccs. 
Distilled water to 3§. 02.) Teo a. 


The plate should remain in this for two or three 
minutes and then be examined by a weak white 
light, and if all the metallic silver has disappeared 
it should be washed for about a minute. It is 
advisable to keep the above reversing solution 
in two separate solutions and mix as required. 

After dissolving out the primary image of 
silver and washing, the plate should be exposed, 
emulsion side up, to white light and then re- 
developed, which may be done by the following 
amidol developer :— 


Sodium sulphite (anhydrous)135 grs. 15 g. 
Amidol . . : 45 » 5» 
Distilled water to 20 0Z. 1,000 ccs. 


The original developer, metol-quinol, rodinal 
etc., may also be used. When the second 
development has completely reduced the silver 
bromide, and the picture now shows up in colour, 
the plate is washed for three or four minutes and, 
without fixing, set to dry. If the plate is seen 
to lack brilliancy (due to over exposure) it may be 
intensified with the following, first immersing 
for not more than ten seconds in 192 minims of 
the permanganate solution given above, diluted 
with 20 oz. of water :— 


Autochromediascope 
(ES “a's ee > 26 grs 30g: 
Citric acid . Aa es, yes 
Distilled water to 20 oz. 1,000 ccs. 
B. Silver nitrate 39 grs 2°5 g. 
Distilled water 3% 02 I0O ccs. 


For use mix 50 minims or 11 ccs. of B with 
I fluid oz. or 100 ccs. of A, and immediately 
apply to the plate and allow to act for three or 
four minutes, then rinse for a minute or two and 
clear in the following :— 


Potassium permanganate 84 grs. 
Distilled water 20 OZ. 


for about one minute, and wash. 
then be fixed in— 


I g, 
1,000 ccs. 


The plate can 


ek ¥pO.” ? GE Rye! 150 g. 
Sodium bisulphite lye Ses BO CCR. 
Water to “ $n 0 1,000 


” » 


for two minutes and washed and dried by a 
gentle heat. When dry it should be varnished 


with— 
Gum dammar 31 gts. 20 g 
Copal. . Gy ae 50, 
Carbon tetrachloride to 34 0z. 1,000 ccs, 
or 
Gum dammar LOz, 20 g. 
Benzole eat 100 ccs, 


When properly treated, and with correct selec- 
tion of the subject, particularly if glaring con- 
trasts of colours are avoided, very exquisite 
results can be obtained. 

Autochromes have been successfully repro- 
duced by the three-colour and four-colour block 
processes by illuminating the transparency with 
reflected light and copying through colour 
filters, the same as in copying from a painting 
or other coloured original. The frontispiece to 
this volume is an example of four-colour repro- 
duction. 


AUTOCHROMEDIASCOPE 

A reservoir viewing instrument for auto- 
chrome and other screen-plate pictures. The 
transparency is viewed, not directly, but reflected 


Autochromediascope 


in a mirror as at A. The plates are held in 
grooves B, and any given one may be brought 
from the grooves (by means of levers C) to the 
open position D, and so receive illumination from 


47 


Automatic Photography 


the sky. A ground-glass screen is placed over 
the opening at the top, in order to diffuse the 
light. ‘The viewing box is mounted on a rotating 
head, by which it can be tilted to any con- 
venient angle. 


AUTOCOPYIST 


A simplified process of collotype, in which the 
glass plates for bearing the printing image are 
replaced by parchment paper, which is coated 
with gelatine, immersed in bichromate solution, 
dried, and exposed under a negative, after which 
it is washed, stretched over a bed-plate, inked 
up and printed from in the usual collotype way. 
The printing is done by means of an ordinary 
letter-copying press, or similar means. 


AUTOGLYPHIC PROCESS 

A method invented by Duncan C, Dallas, by 
which a drawing was made on a metal plate by 
means of a heated pen and a wax composition. 
The plate could be printed from without etching. 


AUTOGRAPHY 

A process of lithographic printing simplified 
for the reproduction of writing in facsimile. 
The writing is done on a hard, smooth-surfaced 
writing-paper with transfer ink, and then trans- 
ferred to stone or zinc in a press. In some pro- 
cesses the paper was damped on the back with 
water; in others with acid, and in one process 
blotting paper soaked in turpentine was applied 
to the back of the sheet. The process has also 
been applied to type-written sheets, and to 
crayon drawings on grained paper. 


AUTOGRAVURE 

A photo-mechanical process modified from 
the well-known photogravure process, the resist 
image being formed by a special carbon tissue 
manufactured by the company that works the 
system. 

Autogravure is also the name of a process 
worked by a firm in Vienna for reproducing 
paintings. Negatives are made for yellow, red, 
blue, and grey printings. Positives are made 
from the first three, and from these half-tone 
negatives are made. These are printed on to 
stone, zinc, or aluminium for lithographic print- 
ing. Further printings are added if necessary 
from the same negatives in other shades of ink. 
From the fourth negative an embossing plate 
is made to give relief to the picture. 


AUTOMATIC PHOTOGRAPHY (Fr., La 
Photographie Automatique ; Ger., Auto- 
matische Photographie) 

A term frequently applied loosely, and refer- 
ring strictly only to apparatus that carries out 
the entire operation of making a finished photo- 
graph. To this class belongs the automatic 
machine exhibited by M. Enjalbert at the Paris 
Exhibition of 1889. Full directions to the sitter 
were shown in turn at the proper times on the 
face of the machine, which was started by drop- 
ping a specified number of coins into a cash-box. 
The duration of the exposure was indicated by 
the ringing and cessation of a bell, and a finished 
ferrotype portrait was delivered in about five 
minutes. Apart from the liability to get out of 
order, the great drawback to apparatus of this 


Automatic Photography 


description is that it cannot make allowance for 
the sitter’s possible inattention to instructions, 
or for variations in light or temperature. Partly 
automatic machines, with an attendant or 
operator, have in consequence enjoyed greater 
popularity. The illustration shows a typical 
so-called automatic camera of the kind used by 
itinerant photographers and at exhibitions 


Automatic Ferrotype Camera 


The box in the centre of the upper shelf is filled 
with forty ferrotype plates in sheaths, which 
may be inserted in daylight, a heavy lid being 
then placed on top to keep them flat. On 
drawing out and returning the rod a, which is 
attached to a plunger, the bottom plate is pushed 
into a horizontal holder. By turning a milled 
head at the side, the plate is raised into position 
for exposure at the back of the small fixed-focus 
camera shown to the left. Having ascertained 
that the sitter is correctly placed by inspecting 
the image in the finder—the small concave lens 
seen at the top—the exposure is made by press- 
ing the bulb, this being connected to a rubber 
tube passing to the shutter through B. Any 
exposure may be given according to the length 
of time the pressure is continued on the bulb. 
By means of another small rod in the side the 
exposed plate is allowed to drop into a wire 
cradle, controlled by the knob c. The cradle 
is raised or lowered by turning the knob, while 
on the attached rod are marked distances to 
indicate how far it must be drawn out to bring 
the cradle over each trough in turn. Having 
allowed the plate to remain in the developer a 
stated time, the knob is turned to raise the cradle 
and the rod is pulled out to the distance marked 
for the fixing bath, in which the cradle is left 
till the plate is fixed. The knob is then again 
turned and the cradle transferred in a similar 
manner to the third or washing tank ; after which 
the panel in the front can be let down to examine 
and remove the plate. With a little practice 
the apparatus is very easily manipulated, a 
finished positive being obtained in about one 
minute, 


48 


Automatic Printing 


Another branch of automatic photography— 
or, rather, automatic exposure—is that in which 
a photograph is obtained by the action, although 
without the concurrence, of the subject, as 
when securing pictures of wild beasts in the 
jungle, or in taking a flashlight portrait of a 
burglar. The latter undertaking is quite feasible, 
and various arrangements have been patented 
for the purpose, in which, for example, the unwel- 
come visitor is supposed to make an electric 
connection by stepping on a mat or opening a 
window, thus rendering a platinum wire red-hot 
and firing a charge of magnesium flash-powder, 
while at the same time actuating the exposure 
shutter of a camera. ‘The one thing against the 
idea is the fact that the modern burglar would 
undoubtedly prevent the survival of the record 
by smashing the camera to pieces. The auto. 
matic photography of animals, birds, and reptiles 
in their natural surroundings is, however, an 
accomplished fact, and some admirable results 
have been obtained. The exposure—or, at 
night, the simultaneous exposure and ignition 
of flash-powder—is usually arranged by causing 
the animal or other subject to disturb an elec- 
trically connected cord, or to make a contact 
by treading on a prepared stone, branch, or twig. 


AUTOMATIC PRINTING (Fr., Impression 
automatique ; Ger., Automatisch Druck) 

As early as 1860, Fontayne, of Cincinnati, 
employed an automatic printing apparatus, by 
which 200 exposures per minute were possible 
upon a band of sensitive paper, a large con- 
densing lens being used to concentrate sunlight 
on the negative. Of later date is a very ingenious 
clockwork printing machine, patented in 1885 
by J. Urie, of Glasgow ; its internal arrangement 


Automatic Printing Machine 


is shown in the illustration. The bromide paper 
is used in a continuous band, which, having once 
been adjusted under the negative, is moved on 
by the length of one print after each exposure. 
The light is furnished by a gas burner, and is 
automatically lowered when the paper travels; 
while a flat dish containing water is interposed 
between the burner and the negative, to prevent 
the overheating of the latter. The correct 
exposure having first been ascertained, the 


BY HENRY W. BENNETT, F.R.P.S. 


IN WESTMINSTER ABBEY 


ARCHITECTURAL PHOTOGRAPHY (INTERIOR) 


Autotype 


machine may be regulated to repeat it inde- 
finitely as long as it will run, and may be left to 
itself. Large automatic printing machines, 
power-driven and electrically illuminated, have 
of recent years been adopted for the production 
in quantities of bromide prints, pictorial post- 
cards, etc. Automatic printing machines of a 
special description are also employed in making 
the positive film from the negative one for the 
kinematograph. 


AUTOTYPE (See “Carbon Process.’’) 


AUTOTYPOGRAPHY (Fr., Autotypographie ; 
Ger,, Autotypregraphie) 

A term sometimes used for relief printing 
blocks, It has been particularly applied to a 
process for the making of prints from the leaves 
of plants and flowers. 

A process called by this name was invented 
by George Wallis, in 1859 and 1860, by which 
drawings made upon gelatine could be trans- 
ferred to metal plates, and afterwards used for 
printing from in the same way as an ordinary 
copper plate. 


AUX DEUX CRAYONS 

A style of stained print once popular in 
America, The print is immersed in a solution of 
alcohol 3 oz., powdered aloes } oz., until stained, 
or toned, a lemon colour, is then well washed, 
and placed in 3 oz. of water to which have been 
added 4 drops of liquor ammoniz. It remains 
there until of a warm orange colour, and is then 
washed, dried, and mounted. The high lights 
ate touched up with Chinese white and the blacks 
with Indian ink, and the whole is finally coated 
with a solution of plain collodion 14 oz., castor 
oil 4 drops. The process is now obsolete, but 
for a time was a craze in the United States, 
where carefully made and artistic examples 
commanded good prices. 


AUXILIARY EXPOSURE 

A method used in the early days of photo- 
gtaphy in connection with slow plates to assist 
exposure. Before or after the proper exposure 
was made, extra exposures were given on coloured 
papers or through coloured. glasses, as it was 
thought that by so doing more detail was 
obtained. In process work even to-day a piece 
of white paper is often placed for a few seconds in 
front of a photograph while it is being copied ; 
while in France it is the custom with some expert 
operators with modern dry plates to expose for 
a second or so upon a piece of white paper 
before photographing dark interiors. It is 
doubtful if such auxiliary exposures are of any 
real use in these days of extra rapid plates, and 
there is always the risk of fogging. Auxiliary ex 
posures have also been advocated for papers, 
particularly when harsh negatives are used, 
for the purpose of getting flatter, actually fogged, 
prints. When photographing gloomy interiors, 
the daylight is utilised as far as possible, and 
sometimes an auxiliary exposure with mag- 
nesium is given for the shadows. 


49 


Azotic Acid 


AUXOMETER (Fr., Auxométre; Ger., Auxo- 
meter) 
An instrument for ascertaining the magnify- 
ing power of a lens or optical system. 


AXIAL ACCOMMODATION OF THE EYE 

In binocular vision, the converging or diverg- 
ing of the axes of the eyes as required so that 
they meet where the object of attention is 
situated. The axis here referred to is the imagin- 
ary line drawn through the centre of the eye from 
the pupillary centre to the retina. In ordinary 
vision, the axes meet at the point where the 
object of immediate attention happens to be 
situated, and as the attention is turned from one 
object to another, the two eyes move by mus- 
cular control, simultaneously, so that whatever 
may be the position and distance of objects 
looked at, the axes converge or diverge as the 
case may require, bringing the attention of both 
eyes to a common point. When the object 
looked at is remotely placed, the eyes look 
almost parallel with each other ; but if the object 
is only a few feet distant from the observer, a 
conspicuous convergence of the axes is noticeable. 
The constant change in the direction of the eyes’ 
axes is known as axial accommodation, and 
without this double images would be seen and 
confusion of perception result. The term is 
sometimes applied to the adjustment of optical 
centres in binocular instruments, such, for 
instance, as the adjustment of twin lenses in a 
stereoscopic camera, binocular microscope, and 
so on. (See “Stereoscopic Photography.’’) 


AZALINE (Fr. and Ger., Azalin) 

A mixture of chinoline red and cyanine, 
introduced as a red sensitiser by H. W. Vogel, 
the use of which has been superseded by the 
newer isocyanines. 


AZOL (Fr. and Ger., Azo/) 

A trade name for a concentrated one-solution 
developer whose action resembles that of rodinal. 
For plates and films 20 minims of azol are added 
to 1 oz. of water. For over-exposure 10 drops 
more of azol per I oz. of water are added, but 
for under-exposure the original quantity required 
is only 15 drops per 1o0z. For bromide papers the 
proportion is 15 drops of azol per 1 oz. of water, 
adding a few drops of a Io per cent. solution of 
potassium bromide if the whites are not pure. 
Gaslight papers need 40 drops of azol per I oz. 
of water and potassium bromide as required ; 
while for lantern slides the developer should be : 
Azol, 25 drops; bromide (10 per cent.), 5 drops ; 
water to I oz. 


AZOTATE 
A term derived from the French and meaning 
nitrate. 


AZOTE 
A French term for nitrogen. 


AZOTIC ACID 
An Anglicised form of the French term for 
nitric acid. 


B 


BACK FOCUS 


A term used to denote the distance between 
the back surface of a lens and the sensitive plate. 
It bears no fixed relation to the true focal length 
of the lens, and the old opticians inserted it in 
their catalogues only as a guide to the camera 
extension necessary. Many of the early cameras 
were sliding boxes, and would not close up 
enough to accommodate all lenses. 


(Fr., Fond; Ger., Hinter- 


BACKGROUND 
grund) 

A term commonly applied to the painted 

sheets or screens used in studio portraiture ; but 

actually the scenery, or anything else, whether 


A. Roller Background 
hung on Brackets 


natural or artificial, behind the sitter or object. 
Studio backgrounds are of many kinds, to suit 
different purposes and tastes; as, for example, 
vignette, full-length, interior, exterior, plain, 
graduated, and cloud backgrounds. They are 
usually painted in oil or distemper on canvas 
or stout paper, and are either attached to rollers 
or stretched tightly on a wooden frame having 
supporting feet. Backgrounds on rollers may 
be hung on brackets like blinds, as shown at A, 
with or without a spring roller, a pulley and cord 
being provided for raising and lowering. In 
another system B the background is fastened 
at the top to a horizontal lath, and is made to 
roll up or down from the bottom by cords passing 
through staples C, or over pulleys, on the same 
principle as theatre curtains are made to work. 


BACKGROUNDS, PRINTING-IN 

The art of using two or more negatives to 
form one print has been widely practised for 
many years. It is sometimes referred to as 
double printing and as combination printing, 
but the former term is generally understood to 
mean the printing-in of clouds (which see), and 
the latter term (fully described under a separate 
heading) the art of combining in one picture 
pieces taken from a number of others. The 
ptinting-in of backgrounds differs from both of 


C. Background Cords 
passed through Staple 


50 


these. It is a common fact that many portraits 
are spoilt by ugly and unsuitable backgrounds, 
but it is possible to take out these and print-in 
more suitable ones. 

The printing-in of backgrounds is easier with 
print-out papers than with development papers, 
such as bromide and carbon, where the progress 
of printing cannot be seen. The simplest method 
is first to block out the background on the original 
negative with an opaque mixture, going care- 
fully round the outline of the figure with a finely- 
pointed camel-hair pencil charged with the pig- 
ment, which may be red water-colour. The 
broad expanse of background may be gone over 
with the pigment on the film side of the negative ; 


B. Background with Roller 
at Bottom 


or Brunswick black, or red or black paper, may 
be used on the glass side. It matters not how 
it is done so long as the background is covered 
up. In the illustrations, A represents a sitter 
against a brick wall which, being quite unsuit- 
able, it is desired to take out. The blocked-out 
negative is printed in the usual way, and will 
give the result indicated at B—that is, the figure 
will have no background whatever. The print 
must not be toned or fixed yet. The selected 
background must next be printed in. To do 
this, carefully paint over the entire figure in 
print B, by gas or lamp-light, with red water- 
colour paint C, well covering the image and care- 
fully following the outline. When quite dry place 
the print in contact with a suitable background 
negative and print in the usual way. The image 
will be printed upon the hitherto blank paper 
only, and the figure will be unaffected owing to 
the protection given by the red pigment (see D). 
Washing the print in water removes the paint 
and gives the result shown at F; this should be 
toned and fixed. Other prints may, of course, 
be made in the same way, but if a number is 
required it will save time to copy F in the camera 
and so obtain a new negative. If a good water- 
colour is used, the portrait image will not be 
injured in any way. If the work has been care- 
fully done, no joins will be apparent. Any slight 


Backings, Plate 


overlapping may be touched out on the finished 
rint. 
Another method of printing-in backgrounds is 
first to block out the background, as in the pre- 
vious case, so as to obtain result B. Print two of 
these. From one the figure is carefully cut out 
with scissors and laid face downwards on the 
background negative. (A print from it would 


id 5 


A. Print with Undesirable 
Background 


resemble E, but this is not the result required. ) 
The second print B is now laid on the prepared 
background negative in such a way that the 
printed figure is covered by the cut-out figure. 
The background is then printed in to give the 
result shown at F. A variation of the process is 
to print in the reverse way—that is, to make 
a print from the background negative (with the 
cut-out figure attached), so as to obtain a print 
like EH, and to use this over the original negative 
with the background blocked out, so as to print 
in the figure B. Either method gives result F. 

Both of the chief methods here described 


51 


Backings, Plate 


which cause halation. Plates may be obtained 
ready backed, many of the commercial back- 
ings being secret preparations and of excellent 
quality. Backings are of many kinds, more or 
less difficult to prepare, apply to, and remove 
from, the plate. 

Liquid Backings.—Any red or black mixture 
will serve for ordinary plates, the latter being the 


A 
A 


B. Print with Background 
Blocked Out 


C. Figure Painted Over 
with Water-colour 


more suitable for isochromatic or colour-sensitive 
plates. Such homely mixtures as red and black 
currant jam and shoe blacking have been 
advocated at various times, but there is no need 
to use such uncertain materials. Brunswick 
black.is good for the purpose, but somewhat 
slow in drying. A quick-drying backing is a 
thin solution of bitumen in benzene, and this 
may be left upon the plate until after the nega- 
tive is developed, fixed and dried, being then 
removed by the aid of benzene. As a general 
rule, backings should be removed before develop- 
ing, because otherwise it is difficult to judge the 


D. New Background 
printed-in ; Figure 
Painted Over 


demand great care, and the first has the dis- 
advantage that some little difficulty is experi- 
enced in getting the two separate printings to 
the same depth. By any of these methods, it is 
difficult to avoid false lighting of the figure. 


BACKINGS, PLATE 
A backing is a coating upon the plain (glass) 
side of a dry plate in order to prevent reflections 


E. Print from Background 
Negative, with Figure 
Blocked Out 


F, Final Result. The Old 
Figure with the New 
Background 


progress of development and the density of the 
image. One of the commercial backings dis- 
solves in the developer without affecting the 
working. Perhaps the best of the home-made 
backings is :— 


Crystal caramel powder . Pee ua) A 
Water . ‘ ; . Fae Sa 
Methylated spirit : Oy 


Backings, Plate 


The ingredients need to be mixed well together. 
Another formula is :— 


Caramel . : ‘ : P62, 
Powdered burnt sienna . ‘ay Sree 
Office gum. : s aa Aa 
For isochromatic plates lampblack should 
be used instead of the sienna. J. S. Teape 
recommends the following :— 
Caramel . ‘ ; ; ve IP OZ, 
Saturated solution of gum traga- 
canth . : , ; I OZ. 
Powdered burnt sienna . BS ihe a 
Methylated spirit . : Sr ere 


The spirit is added after the ingredients have 
been well mixed. The above are liquid back- 
ings, which are in optical contact with the glass. 

Instead of caramel, it is possible to use various 
dyes and pigments, such as sienna, lampblack, 


etc. ‘The following are typical formule :— 
1. Powdered burnt sienna. 4 02. 
Powdered gum arabic . : $ 5, 
Glycerine. 3 : Ae tel 
Water . s : i Seah. tee 
2. Essence of cloves 6 parts 
Turpentine . ; 3 sha et ante 
Lampblack . q.S. 


to form a paste that may easily be distributed 
on the back of the dry plate. 


3. Methylated spirit . IO OZ. 
Soap . : : . - 200 gers, 
Erythrosin I drm, 
Aurin . : : ee eee 


Scrape the soap, and allow it to digest in the 
spirit for a week, shaking at intervals ; filter, and 
add the dyes. This gives a good yellow backing 
solution, which dries at once. 

Paper Backings.—Backing sheets or papers are 
not so effective as liquid backings. Red or black 
paper is cut to size, one side smeared with glycer- 
ine, and pressed into close contact with the glass 
side of the plate. Special backing pads, which 


A. Plates Clipped Together for Backing 


are preferable to the above, may be made by 
coating strong paper with the following mix- 
ture >— 


Gelatine . 3 : : Belk dg so 
Water. ; j : oa WAS 
Glycerine : eee 


Indian ink, sufficient to colour, 


52 


Backings, Plate 


Dissolve by heating, and apply when warm 
to pieces of stout paper or calico, which require 
to be squeegeed on to the backs of the plates, 
and may be used over and over again if smeared 
occasionally with glycerine, 


B. Plate-holder for Use in Backing 


Comparisons.—The following table shows the 
effectiveness of the various backings, the test 
subject being severe :— 

Halation. 
Unbacked plate : . . Very bad. 


Plate backed with— 


Caramel and water . . Very slight. 
Bitumen . ; . . Very slight. 
Sienna and water x « Very slight. 
Black paper and water Bad. 

Black paper and glycerine Not so bad. 
Shoe blacking : : Slight. 

Red and black currant jam Slight. 
Canada balsam and lampblack Nil. 
Caramel and sienna s+ saNaL. 


Films and lantern-slide plates are sometimes 
backed, but they do not show halation so badly 
as dry plates, and therefore the simplest backing 
will serve, if needed at all. (See also “ Hala- 
tion.’’) 

Applying Backings.—The work of backing 
plates must be done in the dark-room, and varies 
somewhat with the nature of the material used. 
It is not absolutely necessary to wait until the 
backing is dry, although it is desirable to do so; 
but if a plate is used with the backing still wet 
it should be covered with paper, preferably the 
oiled kind in which sensitive paper is sometimes 
wtapped. The backing must be applied evenly 


WOMAN NAAM MAA AAA 


* ee eee 
C. Light-tight Drying Box 


and not in streaks, and should cover every part 
of the plain glass side of the plate. The simplest 
method for small plates is carefully to put two 
plates film to film, and to clip them together at 
both ends as at A. The backing may then be 
applied by means of cotton wool or soft flannel 
(brushing causes streaks), and the plates then 


Bag 


hung up or laid aside to dry. In this way, and 
with ordinary care, the backing mixture is kept 
from the films. 

For very messy backings the worker may 
ptefer to use a holder as at B. In the centre of 
a piece of flat wood p, stout enough to prevent 
warping, is glued a piece of black velvet or other 
soft-surfaced material of the size of the dry 
plate. A piece of millboard or of thin wood £, 
of the same thickness as the dry plate and the 
same size as D, to which it is hinged, has at its 
centre a space F of the size of the plate, so that 
when the flap © is placed over the base D the 
velvet is seen through the hole. The plate is 
placed film side downwards upon the velvet, 
and E is brought into position over D, the back 
of the plate coming through F. ‘he backing is 
spread over the plate, any superfluity going on 
to the card. The flap is then lifted up, and 
the plate removed. 

When using slow-drying backings, a dark 
box is convenient, and this can be made with a 
strong cardboard box 1 in. deeper than the 
longest side of the plates to be coated; the 
corners and joints should be covered inside with 
black paper so as to make the box light-tight. 
Place corrugated paper G or strips of cardboard 
along the bottom, as in illustration C, to prevent 
the plates from slipping. The first plate leans 
against the end of the box and supports the 
mext one, a piece of red or black paper being 
interposed. The lid is made light-tight in the 
following manner: Under the edge of the lid 
H glue a strip J, and on Jj glue another strip k, 
covering over the edge of the lid of the box by 
an inch or more. When the lid is put on, the 
box will be quite light-tight, because of the light 
trap formed by Jj and k. 

In process work, it is found that backing the 
plate gives greater freedom from grain between 
the lines or dots, and is quite worth the extra 
trouble. A good backing for this purpose is 
Lichtenstein’s caramel with a little water and 
lampblack added. 

BAG (See “Camera Bag,” ‘“‘ Changing Bag,” 
ete.) 


BAIN-MARIE (EFr.) 


A hot-water bath which in its simplest form 
is that of a jar in a saucepan of water, the 
gelatine, etc,, to be dissolved or melted, being 


Simple Type of Bain-marie or Water Bath 


The ordinary gluepot is an 
example of a bain-marie. The French cook has 
a utensil of the same style and name. A water 
bath of this kind (see illustration) is used by 
photo-lithographers for coa.ing transfer paper. 


placed in the jar. 


53 


Balances 


BALAGNY’S DEVELOPER 
An eatly form of pyro-ammonium carbonate 
developer for dry plates. The formula is :— 


A. Ammon. carbonate 12 oz. 64°5 g. 
Water ‘ Sil. BLOG 7669. 

B. Pyrogallic acid : OL rote 
Ammon. bromide 90 to180 grs. 5°8toI11‘6g. 
Alcohol : 18 oz. 500 ccs, 


For use, mix 6 oz. of A with 1 to 2 drms. of B. 
Under-exposed plates are soaked first in A alone, 
and then in the mixture of the two. 

More recently, Balagny has advocated an acid 
mixture of amidol. (See ‘* Amidol.’’) 


BALANCE IN COMPOSITION (See ‘‘Com- 
position, Pictorial.’’) 


BALANCES (Fr., Balances; Ger., Wagen) 
Weighing instruments. A high degree of 


sensitiveness is not required in the photographer’s 
balances; neither need the instruments be 
expensive. A pair of scales A, or a spring balance 
with pan to weigh up to about 4 oz. or } lb., 


and a smaller balance B, of the kind used by 
pharmacists, will suffice for most photographic 
purposes. Glass pans, preferably removable, 
are best, as it is easier to keep them clean. A 
good balance should possess stability and 


Balloon Photography 


sensibility—that is, it should not oscillate long 
when the two pans are equalised, while a very 
trifling addition on either side should at once 
disturb the equilibrium. 


BALLOON PHOTOGRAPHY (See “ Aerial 
Photography.’’) 


BALSAM 
BALSAMO’S PROCESS (Fr., Procédé Balsamo ; 


Ger., Balsamo’s Prozess) 

A printing process discovered by Prof. J. G. 
Balsamo, of Lucca, in 1861. Phosphorus is 
digested for a considerable time in hydrochloric 
acid at the ordinary temperature, or, to hasten 
matters, at a temperature of about 120° to 140° 
F. (about 49° to 60° C.). The solution improves 
by keeping. When saturated with phosphorus, 
the acid is diluted with copper acetate until the 
liquid assumes an olive green colour. Paper is 
immetsed in this solution in a flat dish for three 
or four minutes, taking care that it is thoroughly 
impregnated, and is then thoroughly dried. The 
paper, which is very hygroscopic, is now exposed 
behind a negative, with a piece of blotting-paper 
at the back to absorb any moisture that may be 
disengaged, until the parts acted upon by the 
light become of a greyish colour, due to the pro- 
duction of copper binoxide, After removal 
from the frame, the print is exposed for about 
five minutes to the vapour of sulphuretted 
hydrogen, which converts the copper binoxide 
into copper sulphide. The print is next washed 
to remove the superfluous copper salts, and is 
then toned in a dilute solution of bismuth nitrate 
acidified with a little nitric acid, by which means 
bismuth is substituted for copper, thus rendering 
the print permanent. 


BARIUM BROMIDE (Fr., Bromure 
baryum; Ger., Baryumbromid) 

BaBr, 2H,O. Molecular weight, 333. Solu- 
bilities 14 in 1 water, soluble in benzole. All 
barium salts are poisonous, and the antidotes 
are sodium or magnesium sulphates followed by 
emetics and the use of the stomach pump. 
Barium bromide is in the form of colourless 
crystals, which are prepared by dissolving barium 
carbonate in hydrobromic acid, evaporating and 
crystallising the solution. It is occasionally 
used in collodion. 


BARIUM CHLORIDE (Fr., Chlorure de 
baryum ; Ger., Baryumchlorid) 

BaCl, 2H,O. Molecular weight, 244. Solu- 
bilities, 1 in 2°5 water, insoluble in alcohol. 
Poisonous (see “‘ Barium Bromide’’). It takes 
the form of colourless flat-sided crystals, which 
are prepared from barium carbonate and hydro- 
chloric acid. It is occasionally used in emulsion 
making, but chiefly in the preparation of barium 
sulphate. 


BARIUM IODIDE (Fr., Iodure de baryum; 
Ger., I[odbaryum) 

Bal, 2H,O. Molecular weight, 427. Solu- 
bilities, 1 in o-5 water, t in 20 alcohol. It is 
poisonous ; for the antidote, see under heading 
“‘ Barium Bromide.” It is in the form of 
colourless crystals, obtained by decomposing 


(See “‘ Canada Balsam.”’) 


de 


54 


Barometer, Photographic 


ferric iodide with barium hydroxide. It is 
readily decomposed on exposure to the air, 
giving off free iodine. Occasionally it is used 
in making collodion emulsion. 


BARIUM MONOXIDE, OR BARYTA (Fr., 
Monoxyde de baryum; Ger., Baryum- 
monoxyda) 

BaO. Molecular weight, 153. A grey, porous 
mass, fusing at a high temperature. It is pre- 
pared by decomposing barium nitrate by heat, 
and is (or was) used in Brin’s process for the 
manufacture of oxygen—the method employed 
in extracting the oxygen for compression into 
cylinders as used by lanternists. 


BARIUM NITRATE (Fr., Azotate de baryum ; 
Ger., Baryumnitrat) 

Ba(NO,),. Molecular weight, 261. Solubilities, 
1 in 12 water, insoluble in alcohol. It is poison- 
ous; for the antidotes, see under heading 
‘* Barium Bromide.” It is occasionally used as 
an admixture in magnesium flashlight powder 
and for making barium monoxide, 


BARIUM PEROXIDE (Fr., Bioxyde 
baryum; Ger., Baryumperoxyd) 

Synonyms, barium dioxide or superoxide. 
BaO,. Molecular weight, 169. Solubilities, insolu- 
ble in water, soluble in dilute acids with de- 
composition, A heavy, greyish-white powder, 
obtained by heating barium nitrate. It has 
been suggested for dissolving the silver image 
so as to obtain reversal, its action being due to 
the formation of nascent oxygen. It also occurs 
in a hydrated form, Ba(OH), 8H,O, having the 
molecular weight, 315, aud being slightly solu- 
ble in water. 


de 


BARIUM SACCHARATE (Fr., Suwucrate de 
baryum ; Ger., Zuckerbaryt) 
Soluble in water. It is poisonous; for the 


antidotes, see under heading “* Barium Bromide.” 
It occurs in white crystals, but a solution was 
suggested by Mathet as a substitute for the alka- 
lis in developers. Excess of barium hydrate is 
shaken for several days with a 10 per cent. 
solution of sugar and then filtered; but it has 
found no practical use. 


BARIUM SULPHATE (Fr., Sulfate de baryum ; 
Ger., Schwefelsaures baryt, Schwerspat) 

Synonyms, barytes, synthetic barytes, blanc 
fixé, permanent white, baryta white, mountain 
snow. BaSO,. Molecular weight, 233. Solu- 
bilities, insoluble in water and alcohol. It is a 
heavy, white, impalpable powder, occurring 
naturally or prepared by adding sulphuric acid 
or a soluble sulphate to a soluble barium salt. 
It is used to prepare baryta paper (which see), 
the very commonly used paper for silver print- 
ing processes. 


BAROMETER, PHOTOGRAPHIC 


Photographic prints that act as weather 
indicators; known also as weather-glass prints. 
Certain coloured photographs will alter with 
the varying atmospheric conditions, owing to 
the fact that cobalt chloride (CoCl,) has been 
used in preparing them, this salt being blue 
when anhydrous (perfectly dry) and pink when 


Baryta 


damp. Cobalt solutions may be used as sym- 
pathetic inks, the writing being almost invisible 
until warmed before a fire and all moisture 
driven out, when it becomes blue. A finished 
but unmounted bromide print is soaked for ten 
minutes in a 5 per cent. solution of formaline, 
and then is washed and dried. The cobalt 
solution is made as follows :— 


Gelatine 4 oz. 68 g. 
Glycerine ren 250 ccs. 
Cobalt chloride 40 gts. 23 2. 
Water : : fr a) OS. OOO Ses, 


The gelatine (ordinary cooking gelatine will 
serve) is soaked in the water until swollen, and 
is then melted by gentle heat ; then the glycerine 
is added and next the cobalt chloride. The 
warm solution is brushed over the bromide print 
that has been previously treated with the forma- 
line. The print is drained, dried, and hung up 
unframed or in an unglazed frame. The print 
is of a pinkish colour in wet weather, blue in dry 
and fine weather, and of a lilac or lavender colour 
in changeable weather. 


BARYTA (See “‘ Barium Monoxide.’’) 


BARYTA PAPER (Fr., Papier baryté; Ger. 
Barytpapier, Kreidepapier) 

Good raw paper stock coated with an insoluble 
emulsion of baryta in gelatine and used princi- 
pally for coating paper intended to take a gela- 
tino-chloride emulsion, A good baryta paper 
must be coated with three films, the first two 
serving to prevent the emulsion from coming 
into contact with the paper and the third giving 
the particular surface and tint desired. Both 
glazed and matt surfaces, tinted red, blue or 
violet, or white, can be obtained. It is also 
used in surfacing paper for collotype and Wood- 
burytype. 

Its preparation requires costly machinery. 
The baryta is either precipitated by the paper 
coater, or bought in the form of powder and 
mixed in a kneading machine with one-third its 
weight of water till a perfectly uniform cream is 
obtained, which is carefully sifted, divided into 
two equal parts, and thoroughly mixed with 
gelatine solution. To one part of the baryta 
emulsion is slowly added, with constant stirring, 
a solution of chrome alum, which causes the 
emulsion to become ropy, and at the moment 
of this appearance the other half of the baryta 
emulsion is added. The mixture is again passed 
through sieves, some glycerine added, and then 
coated on the paper. The first coating is 
so adjusted that there is about 12 to 15 g. of 
dry baryta to every square meter (17 to 21 grs. 
per square foot). The emulsion is picked up 
by the paper, which is coated in long rolls, 
by passing through a trough, or it is wiped on 
by a roller, and it then passes over a rubber- 
coated cylinder ; evenness of coating is obtained 
by seven brushes with reciprocating motion, the 
first being hard and the others gradually in- 
creasing in softness until the seventh is of the 
very finest and softest badger hair, about 2 in. 
long. The paper is then hung in festoons to 
dry, rolled up, and given the second coating in 
precisely the same way. Sometimes it is then 
calendered, but usually again coated by the 


55 


Baskett’s Reducer 


same machine with another baryta emulsion 
containing glycerine and chrome alum, and 
more or less gelatine, according to the surface 
desired. To this emulsion is also added the 
colouring matter—Paris blue, ammoniacal car- 
mine solution, etc., being used. After drying, 
the paper is passed through calendering machines, 
which are provided with heavy steel rollers, 
which may, or may not, be heated, and exert 
a pressure of about 10,000 lb. The paper is 
sprayed with water before passing through the 
calender rolls, and the surfaces of the latter are 
highly polished, roughened, or grained respec- 
tively, so as to impart a special surface to the 
baryta film. 

The commercial baryta paper is usually obtain- 
able in rolls of about 600 metres in length, and 
is graded according to surface—matt, glossy, 
rough or grained—and according to the weight 
in grammes per square meter. 


BASEBOARD (Fr., Base ; Ger., Bodenbrett) 


The board serving as the foundation of any 
apparatus, particularly of a camera. Except in 
studio and process cameras, it is generally 
hinged to the body, in order to fold up; and it 
is provided with a bush to take the screw attach- 
ing the camera to the tripod stand, or with a 
circular turntable, which can be fitted on the 
legs of the latter. The stability of the baseboard 
is a vital consideration for serious work, especi- 
ally that of a scientific or technical nature, and 
for such the studio pattern of camera is pre- 
ferable, where it may be used. 


BASKETT’S REDUCER 

A mechanical abrading reducer for negatives 
and lantern slides, introduced by Robert Baskett 
in 1901 ; known also as the Globe polish reducer. 
The formula is :— 


Terebene : : : 2 OZ. 
Salad oil : : , Pale ear 
Globe metal polish . « One 2d, tin. 


The terebene is sold at oil and colour shops as a 
paint drier at about eightpence per pint ; the re- 
fined spirit, costing about one shilling per ounce, 
is not required. The ingredients are well mixed 
together and strained once or twice through fine 
muslin into a bottle. When required for use, 
shake up the mixture, put a few drops on a piece 
of cotton wool or chamois leather, and rub 
gently and evenly over the parts of the negative 
(which must be perfectly dry) to be reduced. 
Rub with a circular motion and not too hard, 
as it is easy to rub a hole in the film. When the 
surface reduction has proceeded far enough and 
the surplus grease has been wiped off with a piece 
of clean cotton wool, a final rubbing with a pad 
slightly moistened with benzene will give a 
polished and nearly waterproof surface that is 
with difficulty distinguished from the glass side 
of the negative. Alcohol will also clean off the 
superfluous reducer. The reducer is particularly 
suitable for local reduction when only a part of 
a negative and not the whole is to be reduced. 
Some kinds of liquid metal polishes, which are 
put up in convenient metal bottles, can be used 
as reducers exactly as bought. 

Alcohol used in the same way as this reducer 
acts similarly, but takes very much longer, 


Bas-reliefs 


BAS-RELIEFS 

Plaster or wax casts in low relief produced 
from photographs ; formerly they were popular 
for brooches, cameos, etc. Generally, the relief 
obtained is very small. The process depends 
primarily upon the hardening action of light 
upon gelatine impregnated with potassium 
bichromate. A negative should be specially 
taken for the purpose of the first experiments, a 
suitable subject being a modelled bust or a 
sculptured bas-relief. I,andscapes are prac- 
tically impossible subjects; while portraits 
should not be attempted unless the sitter’s face 
and hair have been powdered to imitate a bust, 
great care has been taken with the lighting, and 
the photograph has been taken in the brightest 
possible light against a perfectly black back- 
ground. Any heads attempted should not 
exceed 3 in. in height, as the relief obtained is 
not sufficiently strong for larger sizes. Success 
depends upon the contrasts in the negative, and 
if not sufficient these should be increased by local 
intensification or by working on the back of the 
negative. 

Having obtained a suitable negative, a sheet 
of No. 4 gelatine is soaked in a solution of 1 drm. 
of potassium bichromate in 6 oz. of water. The 
swollen gelatine is next squeegeed on to a well- 
waxed glass plate and dried slowly in the dark, 
it being then stripped from the glass and its 
polished side printed upon from the negative. 

An alternative method of preparing the 
bichromated gelatine is to soak 5 oz. of gelatine 
(Nelson’s No. 1) and 2 oz. of powdered gum 
arabic for four hours in a mixture of 6} oz. of 
acetic acid and 18} oz. of water; at the end of 
the four hours dissolve by gentle heat, strain 
through clean linen, and coat some polished 
glass plates with it, avoiding air-bubbles and 
dust. Dry the plates in a well-ventilated dark- 
room as rapidly as possible, maintaining the 
temperature at from 50° to 75° F. (10° to 24° C.). 

Hither gelatine sheet or plate is printed by 
daylight in contact with the special black and 
white negative. Exposure depends upon the 
strength of light and density of the negative, 
the average duration being thirty minutes. ‘The 
gelatine shows a faint image, which is a slight 
guide. 

The gelatine sheet, after printing, is cemented 
firmly, face upwards, to a piece of glass, by means 
of liquid glue or similar adhesive, and the whole 
is then soaked in cold water for several hours, 
at the end of which time the parts acted upon 
by light are found to have lost their power of 
absorbing water, while the other parts swell 
considerably, If the relief is not sufficiently 
pronounced, it may be increased by soaking in 
a solution of 1 oz, of citric acid in 4 oz. of water 
and transferring to water. When swelled as 
much as possible the superfluous water is drained 
and removed with bDlotting-paper, some oil 
poured on and drained off, and it is then ready 
for casting from. 

In the case of a glass plate instead of the 
gelatine sheet, after printing it is soaked in a 
solution of 2 oz. of powdered alum and 30 drops 
of glacial acetic acid in 40 oz. of water. At the 
end of two hours a fairly good relief should be 
secured, If the relief is not enough the negative 
may have been unsuitable, the exposure under 


56 


Bas-relief Prints 


the negative not long enough, or the plate 
dried too slowly after sensitising. The super- 
fluous moisture is blotted off and the relief oiled. 

Whichever method has been employed, the 
result so far is an oiled gelatine mould, from which 
a cast is now to be made in plaster-of-paris or 
wax. The mould is placed in an old printing 
frame or a tray; or, instead, wceoden sides 
are built up round it to form a receptacle for 
the plaster. All surfaces which the plaster will 
touch, except the relief itself, should now be 
smeared with vaseline. Mix up some perfectly 
fresh plaster-of-paris to about the consistency 
of cream, immediately strain through muslin, and 
without losing time pour on to the oiled relief to 
a depth of 4 in. When the plaster has set it 
may be separated from the relief and the latter 
used again after soaking in water and oiling. 

In addition to plaster, stearine, spermaceti, 
and even heavy brown wax, make excellent 
casts. Coloured waxes may be made according 
to the following formule (given by H. E. Black- 
burn): Red.—Wax 500 grs., India red 64 grs., 
carmine lake 90 grs. Sepia.—Wax 500 grs., 
sepia 50 gts., lampblack 10 grs. Gyveen.—Wax 
500 gts., cobalt blue 10 grs., Indian ink 50 grs, 
Blue.—Wax 500 grs., Frankfort blue 100 grs., 
alizarin blue 15 grs., Indian ink 50 grs. Warm 
black.--Wax 500 grs., lampblack 50 grs., burnt 
umber 60 grs., indigo 32 grs. If desired a thin 
layer of wax of one colour may be brushed on 
the mould, allowed to set, and the mould then 
filed up with wax of ancther colour. The 
plaster gives more permanent results, 


BAS-RELIEF PRINTS 

Photographic prints embossed in low relief. 
Platinotype prints are the best for this purpose, 
but others may be used if hardened in a 10 per 
cent. solution of formaline. A folding wooden 
frame A is required large enough to take an 
unmounted print. The opening in the frames 


B. Bas-relief 
Print in Folding 
Frame 


A, Folding Frame used in 
making Bas-relief Prints 


must be as large as the actual portrait, but smaller 
than the complete print. Profile portraits give 
the best results. On a piece of cardboard the 
same size as the print, is traced the outline of 
the head and bust; to do this, trace the head 
on a piece of tracing paper and transfer to the 
cardboard by means of carbon (manifolding) 
paper. Cut out the space inside the outline, 


Baths 


and the card will then form a mask, which should 
exactly correspond with the outline of the 
portrait. The print is now mounted on thick 
blotting-paper with starch or other slow-drying 
adhesive, and is placed under heavy pressure 
for ten or fifteen minutes, after which time it 
should feel damp and pliant. Some workers wet 
the blotting-paper to ensure this. The cut-out 
mask is next placed over the face of the print 
in register, and the whole put into the frame 
and clamped. The arrangement is shown by B, 
the bust being seen through the hole in the card. 
By means of a bone or ivory paper-knife, or 
the handle of a tooth-brush, carefully apply pres- 
sure from the blotting-paper side and raise or 
emboss those parts desired, holding the frame 
in the left hand and working with the right, the 
face of the print being nearest the operator. 
First of all work the tool all over the back of 
the portrait with a circling motion, and then 
apply more pressure to the nose, cheeks, dress, 
etc., which need to be given in prominence. The 
work must be done very gently, as the blotting- 
paper is damp, and the tool may go through 
the picture and spoil it. Leave in the frame 
until dry and mount on stiff card by the edges 
only. (For imitation bas-reliefs, see ‘‘ Plastic 
Photographs.’’) 


BATHS (Fr., Bains ; Ger., Bader) 


A name given both to the trays, dishes, or 
troughs holding photographic solutions, and to 
the solutions themselves. Thus, the dish used 
in fixing is known as the “ fixing bath,” a term 
also applied to the “hypo” solution which it 
contains. Baths may be either upright (as, for 
example, the silver bath in the wet collodion 
process), or horizontal (as, for example, the 
dishes or trays for developing, toning, and fixing). 
Dishes and trays are made in many different 
materials, such as porcelain, stoneware, “ grani- 
tine,’ glass, enamelled iron and steel, papier 
maché, vulcanite, celluloid, zinc, lead, etc. 
Glass dishes and dishes coated with vitreous 
enamel have the advantage that they are unaf- 
fected by chemicals, readily cleaned, and show 
distinctly any lack of cleanliness. But porcelain 
dishes are commonly preferred for most purposes, 
although they will not resist all chemicals. For 
developing, ebonite or celluloid dishes are pro- 
bably most convenient; for toning and fixing, 
porcelain or glass; while enamelled iron or steel 
is used for hot-bath platinotype. Lead or stone- 
ware troughs and trays are employed to resist 
acids. 


BAUDRAN’S 
METHOD 
A method of projecting ordinary uncoloured 
photographic prints on to a surface whereon 
they are said to appear more or less coloured. 
It was invented by Baudran, of Versailles, in 
1891. It is well known that some daguerreo- 
type pictures show a trace of natural colour when 
viewed at a certain angle, and Baudran thought 
that by properly lighting ordinary pictures on 
silver paper he could obtain colours in the same 
way. An opening is made in the shutter of a 
dark-room, and on a shelf outside is placed a 
photograph, preferably an enamelled print on 
albumen paper, facing the opening and cutting 


COLOUR PROJECTION 


57 


Bedford, Francis 


off much of the light that would otherwise be 
admitted. A mirror is so placed as to reflect light 
upon the photograph, the object being to light 
the image in the same way as the original sub- 
ject was lighted. In the opening in the shutter 
is placed a camera which projects an enlarged 
lmage on a screen inside the dark-room. The 
image is said to be coloured. All colours do not 
appear equally well, but that of the flesh is 
said to be visible mostly always, although not 
very bright. 7 


BEACH’S DEVELOPER 

A pyro-potash developer popular at one time, 
particularly in the United States, where it was 
originally introduced by F. C. Beach. It gives 
a clear negative and a fine black image, which 
was considered preferable to the yellowish, 
slow-printing negatives produced by the pyro- 
ammonia developer. The inventor appears to 
have modified his developer a number of times, 
but the chief ingredients were always pyrogallic 
acid, sodium sulphite, acid and potash. The 
best way to make up the two stock solutions is 
described below, the actual formula being :— 


No. 1 (pyro solution)— 


Water : 5 Oz 142 Coss 
Sodium sulphite hr eR RAY Oe 
Sulphurous acid ag one 
Pyrogallice acid Fong ict BRA coe: 
No. 2 (potash solution)— 
Potassium carbonate 3 Oz 93 g 
Sodium sulphite Tee A GH x, 
Hot water to $55, 284 ccs 


For the pyro solution the water is boiled and 
the sodium sulphite dissolved therein. When cold 
the sulphurous acid (dilute, as sold by chemists) 
needs to be added, and finally the pyro. Beach’s 
original method of making the potash solution 
was to dissolve the carbonate in 44 oz. of hot 
water, the sulphite in 4 oz. of hot water, and 
to mix the two. The above are stock solutions, 
which will keep good for a long time. To make 
a working developer, take 1 oz. of water, add to 
it 1 drm. (60 minims) of the potash (No. 2) 
solution, and from 20 to 30 drops of the pyro 
(No. 1) solution, Add bromide in cases of 
over-exposure, 


BEAUME DEGREES (See “ Hydrometer.’’) 


BECQUEREL RAYS 

Very shortly after the discovery of the 
Réntgen rays, H. Becquerel discovered that the 
metal uranium, its earths and compounds, 
emitted rays which penetrated wood, glass, and 
even some metals, and exerted an action on a 
dry plate similar to that of light. He proved 
that the richer an earth or compound was in 
uranium the stronger were the rays emitted, 
and this led to an examination of pitchblende 
by M. and Mme. Curie, who finally isolated 
radium from the uranium pitchblende and 
proved that to this were due the Becquerel rays, 


BEDFORD, FRANCIS 

Francis Bedford (b. 1816, d. 1894) was asso- 
ciated with photography since its first practical 
inception, and had such skill as a landscape 
worker that he was invited to form one of the 


Beechey’s Process 


party selected to accompany the late King 
Edward (then Prince of Wales) when he visited 
the East in 1863. His son William (b. 1847, 
d. 1893) was President of the Bath Convention, 
1891. 


BEECHEY’S DRY PLATE 
PROCESS 

A method of preparing collodion dry plates, 
published by the Rey. Canon Beechey in October, 
1875, further details appearing in 1879. The 
plates were coated with a collodion made accord- 
ing to the following directions: First prepare 
a solution of cadmium bromide 32 grs., alcohcl 
1oz. Decant after standing for some time, and 
add hydrochloric acid 8 minims. Next take 
above solution 4 oz., absolute ether 14 0z., 
pyroxyline 12 grs. The plates having been 
coated with this are next sensitised in an 
alcoholic silver nitrate bath (40 grs. to the ounce), 
the plates being previously given a substratum of 
gelatine or indiarubber. They are then soaked 
in a solution of 20 grs. of pyrogallic acid in 20 oz, 
of flat bitter beer, which acts as a preservative. 
Great latitude is allowable in the exposure, from 
thirty seconds to five minutes being common. 
The following developer was specially recom- 
mended :— 


Potassium bromide (12 grs. per 


(EMULSION) 


1 oz. solution) p . 15 drops 
Pyrogallic acid (96 grs. solu- 

tion) ‘ : ; ir ee. 8 Nee 
Ammonium carbonate (60 grs. 

solution) . ‘ 3 drims. 


The plates were an article of commerce for many 
years, and were very popular for transparency 
work, 


BEER DRY PLATES 

Dry collodion plates at one time used chiefly 
for positive (lantern-slide) work. The plates 
were sensitised in the usual way, washed, coated 
with beer, and dried. Further information will be 
found under the following headings: ‘‘ Albumen 
Process,” ‘‘Beechey’s Dry Plate (Emulsion) 
Process,’ and ‘Coffee Process.’’ The beer, 
coffee, etc., acted as preservatives. 


BEESWAX (Fr., Cire ; Ger., Bienenwachs) 

A wax obtained from the honeycomb of the 
bee. Melts at 62° to 65° F. It is insoluble in 
water and alcohol, but, if pure, entirely soluble 
in hot oil of turpentine. The wax when pure 
is a yellowish mass of a pleasing smell, and 
breaks with a granular structure. It is used in 
some processes of carbon printing. White wax 
should be ordinary beeswax bleached by exposure 
to sunlight and air. 

In process work, beeswax forms an important 
ingredient in the composition of etching inks. 
A dusting-on powder, known as waxed asphal- 
tum, for photo-lithographic half-tone transfers, 
consists of beeswax and asphaltum melted 
together and powdered. Beeswax (preferably 
the best Gambia) is largely used in electrotyping, 
for making the moulds from blocks or type. 


BELITSKI’S REDUCER 


A one-solution reducer for negatives, known 
also as the “‘ green’? reducer. The formula is :— 


58 


Bennett’s Carbon Sensitiser 


Potassium ferric oxalate 150 grs. 
Sodium sulphite 12904 
Water : 5 7 OZ. 


Shake until dissolved, and add oxalic acid 40 
to 45 gts. Shake again until the solution turns 
green, pour off the solution from any undis- 
solved crystals, and add hypo 1? oz. Instead 
of the potassium ferric oxalate, which is at 
times difficuit to obtain, 100 grs. of ferric 
chloride crystals and 190 grs. of potassium 
oxalate may be used. The reducer is usable 
over and over again, does not stain, and keeps 
well in the dark. 


BELLOWS (Fr., Soufflet ; Ger., Balg) 

The light-tight, collapsible, or expanding con- 
nection between the back and front of the 
camera, usually made of leather or American 
cloth lined with black fabric. There are various 
shapes, as, for example, square A, oblong, 
conical (or, more correctly, pyramidal) C, 
stereoscopic B, truncated-cornered D, and others. 
The square bellows is generally preferred for 
studio, process, and scientific apparatus. The 
lighter and handsomer pyramidal bellows, now 


B. Stereoscopic 
Bellows with Division 


Bellows 


D. Bellows with 
Truncated Corners 


C. Conical or 
Pyramidal Bellows 


almost universally seen on field and hand cameras, 
may sometimes cut off a part of the view when 
using the rising front, unless care is taken. The 
oblong bellows is practically out of date, except 
for stereoscopic cameras, owing to the intro- 
duction of the reversing back. The stereoscopic 
bellows, which may be either oblong or pyra- 
midal, is provided with a central partition fold- 
ing in unison with the bellows. <A bellows with 
truncated corners has the advantages that it 
closes in smaller space, is more elastic, and the 
folds are less liable to cling together. 


BENNETT’S CARBON SENSITISER 
A solution for sensitising the carbon tissue 


supplied in an insensitive condition; intro- 

duced by H. W. Bennett. The formula is :— 
Potassium bichromate . 4 drms. 22g 
Citric acid . ; POE Hc Cer 
Strong ammonia (about) 3 drms. 16°5 ,, 
Water . 25 Oe 1,000 ccs. 


The proportion of water may be varied, any 
quantity from 10 oz. to 25 oz. being used; the 
smaller quantity of water makes the tissue more 


Bennett’s Reducer 


rapid, but it gives less contrast in the print, and 
the full quantity is better for ordinary work. 
The quantity of ammonia is only approximate ; 
it must be determined by the amount neces- 
sary to change the colour of the solution from 
the deep orange of the bichromate to a distinct 
lemon yellow. To sensitise, the piece of tissue 
should be immersed in the solution for two 
minutes, withdrawn, laid on a piece of glass or 
ferrotype, squeegeed to remove as much of the 
solution as possible, and then lifted from the 
glass and pinned to a lath by two corners, or 
suspended from a cord by clips, so as to hang 
freely exposed to the air to dry. Drying should 
be accomplished in from four to six hours. 
Sensitising may be done in full daylight, but 
drying must take place in the dark. 

Tissue sensitised in this solution will render 
gradation much more perfectly, especially in 
the lighter tones. A little gaslight in the drying- 
room will have no effect on the quality or solu- 
bility of the tissue ; even a considerable amount 
of gaslight will be practically negligible. Details 
of working are given under the heading “‘ Carbon 
Process.” 


BENNETT’S REDUCER 

A well-known reducer, introduced by H. W. 
Bennett, made by adding sodium sulphite to a 
solution of ammonium persulphate, and acidify- 
ing by means of sulphuric acid. Reducing by 
means of this reagent is reliable and uniform in 
its results; the operation is free from the risk 
of staining and other irregularities which pre- 
viously made the ammonium persulphate reducer 


uncertain. The formula is :— 
Ammonium persulphate I oz. 118g. 
Sodium sulphite - oS gts: Bata 
Sulphuric acid ies. 2OUUS, | TO ¢cs. 
Water to make 9} 0z. 1,000 ,, 


(For working details, see “Reducing Negatives 
by Chemical Means.’’) 


BENNETT’S TONING 
P.O.P. 

A combined toning and fixing bath that gives 
rich purple tones on most brands of P.O.P., 
introduced in 1908 by H. W. Bennett. It con- 
tains a sufficiently large proportion of “‘ hypo ”’ 
to ensure perfect fixation of the prints, and the 
bath is rendered slightly alkaline with ammonia. 
Prints toned and fixed in this bath are as per- 
manent as any silver prints; they preserve their 
original richness and freshness unimpaired for 
many years. A feature of the bath is the fact 
that separate solutions are kept of each ingre- 
dient, and they are so adjusted that equal 
quantities of each are taken, excepting the 
“hypo” solution, and 1 oz. of that is required 
for each dram of the others. No calculation is 
needed, whatever quantity of solution may be 
required. Five solutions are necessary :— 

A. Sodium hyposulphite Ib. 

Water, sufficient to make 32.0, 


The “hypo” should be dissolved in boiling 
water. 


BATH FOR 


B. Ammonium sulphocyanide . 2 oz. 
Water to make ‘ ai BES. 
C. Lead acetate . 3 ° They 
Boiling water to make 84 ,, 


59° 


Bennett’s Toning Bath 


A dense precipitate will settle. The bottle 
must be well shaken each time any solution is 
required. 


D. Gold chloride  . I5 grs. 
Water : 2 0z. 7 drms. 

E. Strong ammonia . 120 mins. 
Water to IO Oz, 


Each solution will keep indefinitely. To pre- 
pare the bath, mix together in the order given: 
1 oz. of A, 1 drm. of B, 1 drm. of C, 2 oz. water, 
1 drm. of D, and 1 drm. of E. The measure 
must be thoroughly rinsed after measuring 
C and D. The solution is ready for use in five 
minutes. This quantity is sufficient for ten 
quarter-plate prints; a suitable quantity for 
any other number may be prepared by allow- 
ing 4 oz. of A for every five quarter-plate 
prints, and remembering that whatever number 
of ounces of A solution are taken, the same 
number of drams of each of the others will 
be required. The prints are immersed in the 
bath without previous washing, and they should 
be put in the solution one at a time, and each 
one thoroughly wetted before the next is added. 
All the prints that are to be toned in one dish 
should, however, be put into the solution as 
quickly as possible consistently with covering 
each with the solution evenly. 

As soon as the last print is placed in the dish 
the first should be taken from the bottom, 
brought to the top, and quickly examined. 
Should any air-bells have formed on the surface 
they will show as dark marks; but if they are 
broken at once with the finger they will not show 
on the finished print. The second print that 
was placed in the bath will now be the lowest ; 
this should be brought to the top, and so on with 
each print in turn, until all have been changed 
in position. Throughout the operation the same 
method of procedure must be followed—the 
lowest print brought to the top; but after the 
first changing the work should proceed more 
leisurely, leaving each print a longer time at the 
top of the solution. The minimum time of 
immersion in the bath is twelve minutes in hot 
weather if the temperature of the solution is 
70° F, (21° C.) or more, and fifteen minutes in 
cool weather, though the toning should not be 
done in a room at a lower temperature than 
about 60° F. (15°5° C.). This minimum time is 
very important; if less time in the solution is 
given, imperfect fixing will result. Longer time 
may be allowed if cooler tones are desired ; 
twenty minutes will not be too long. If warmer 
tones are required, the composition of the bath 
must be varied, so that the desired tones are 
not reached before the prints are fixed. The 
amount of water used for making the B and C 
solutions may be increased to 11 oz., and for 
the D solution 3 oz., and the bath still pre- 
pared by taking 1 drm. of each for 1 oz. of A. 
As soon as the minimum time has elapsed, or 
the desired tone reached if longer than the 
minimum time, the prints are taken from the 
bath and at once well washed. If washed in 
water that is frequently changed, from one to 
two hours should be allowed, according to the 
frequency of the changes and the quantity of 
prints in one dish. Prints for this toning bath 
require to be very deep. 


Bennetto’s Colour Photography 


BENNETTO’S COLOUR PHOTO- 
GRAPHY 

A process of three-colour photography in 

which the three negatives were obtained at one 

exposure in a camera, the positives being 

made on red, yellow, and blue carbon tissues 

and superimposed. It has not been commer- 


cially introduced. 


BENZENE (Fr., Benzol, Benzine crystallisable ; 
Ger., Benzol, Steinkohlenbenzin) 

Synonyms, benzol or benzole, coal tar naphtha, 
phenyl hydride. C,H,. Molecular weight, 78. 
Solubilities, insoluble in water, soluble in alcohol, 
ether, chloroform, acetone, and glacial acetic 
acid. The vapour is extremely inflammable. 
It is a colourless, mobile, volatile liquid, which 
can be obtained from benzoic acid, but is usually 
procured by distillation from coal-tar. It is 
used in varnishes and for developing in the 
bitumen process, 

This substance must not be confounded with 
benzine or benzoline (which see). A crystal of 
iodine dropped into benzene turns carmine- 
coloured, whilst with benzine a violet colour is 
obtained. A drop or two of absolute alcohol 
will not mix with benzine, but mixes at once 
with benzene. 

In process work, benzole is used for dissolving 
indiarubber to make the solution used in edging 
wet collodion negatives, and for coating the 
latter as a preliminary to applying collodion for 


stripping. It is the best solvent for asphaltum. 
BENZINE (Fr., Benzine, Ger., Benzin 
Petroleumbenzin) 


Synonyms, benzoline, petroleum ether, naph- 
tha, petroleum naphtha; practically identical 
with petrol and gasolene. It is a colourless 
liquid obtained from petroleum by distillation. 
It is rarely used in photography, and must not 
be confounded with benzene (which see). 


BENZOATE TONER 

One of the many toners recommended in 
bygone days for plain salted paper. The follow- 
ing is a typical formula, and gives black-violet 
tones :-— . 


Ammonium benzoate 30. grs, .» 412g. 
Gold chloride : A ree SS Bits 
Water 16 Oz. 1,000 ccs. 
BENZOIC ACID (Fr., Acide benzoique; Ger., 
Benzoesdure) 


Synonym, phenylformic acid. C,H; COOH. 
Molecular weight, 122. Solubilities, 1 in 15 
boiling water, 1 in 1-8 alcohol; soluble also in 
ether, chloroform, glycerine, benzole, fixed and 
volatile oils. Borax or sodium phosphate 
increases the solubility in water. It occurs as 
white or faintly yellowish pearly plates o1 
needles with agreeable aromatic odour and 
taste, and is obtained by sublimation from gum 
benzoin, or from toluene by oxidation with nitric 
acid, or from the urine of herbivorous animals 
by distillation. 


BENZOLE (See ‘‘ Benzene.’’) 


BENZOLINE (See “ Benzine.’’) 


Berkeley’s Sulpho-Pyrogallol 


BENZOQUINONE, OR QUINONE 

C,H,O,. Molecular weight, 108. Slightly 
soluble in water, more so in alcohol and ether. 
It forms volatile yellow prisms, plates, or needles, 
having a pungent smell. It is procured com- 
mercially by acting on aniline with a bichromate 
and sulphuric acid. It is used in the preparation 
of the developer hydroquinone (benzoquinol, or 
quinol, C,H,(OH),), a substance which is ob- 
tained by the reduction of quinone with sul- 
phurous acid. 


BERGHEIM LENS 

This lens was constructed in 1896 by T. R. 
Dallmeyer at the suggestion of J. S. Bergheim, 
a painter, who wished for a lens which would 
give him correct drawing and soft definition 
without sacrificing the natural structure of the 
original, ‘To obtain this end the inventor intro- 
duced a large amount of both spherical and chro- 
matic aberration, so that to obtain the maximum 
Sharpness possible with this lens an allowance 
has to be made after focusing. Although prim- 
arily intended for portraiture, the Bergheim 
lens is constructed on the telephoto principle, 
the front element B being a single uncorrected 
positive lens, while the back is an uncorrected 
negative lens c of similar focal length—that is 
to say, when the two lenses are brought into 
contact they neutralise each other, various 
focal lengths being obtained by separating them. 


T 


A c 
Bergheim Lens 


The greater the separation the shorter is the 
resulting focal length. The diaphragm 4 is fixed 
in the hood of the lens, and is marked for aper- 
tures requiring certain fixed relative exposures, 
no matter what the temporary focal length 
may be. The characteristic feature of the 
definition given by this lens when skilfully used 
is a pleasing semi-sharpness through a very deep 
field, no actual sharpness or offensive fuzziness 
being visible. 


BERKELEY’S SULPHO-PYROGALLOL 


The first of the developing substances to be 
preserved in solution by means of an acidified 
sulphite ; it was introduced by H. B. Berkeley, 
in 1882, 

Berkeley’s solution consists of 4 oz. of sodium 
sulphite with sufficient citric acid (about } oz.) 
to render the solution distinctly acid; 1 oz. 
of pyro is dissolved in 9 oz, 55 minims of the 
solution, so that every 10 minims contain 1 gr. 
of pyro. The sulphite must be thoroughly 
dissolved in the water, and the solution acidified 
before the pyro is added. The introduction of 
sulphite as a preservative of pyro in solution 
has been of great service to photographers. The 
sulphite not only preserves the developing sub- 
stance in solution, but prevents the rapid 
oxidation of the developer in use, thus keeping 


Bichromate 


the plate clean and free from stain. Without 
sulphite the use of pyro with the alkaline car- 
bonates would be impracticable, on account of 
the very rapid discoloration of the developer 
and the excessive staining of the plate. 

The use of an acidified solution of sodium 
sulphite as a preservative has been largely super- 
seded in the case of pyro by the introduction of 
potassium metabisulphite, a strongly acid sul- 
phite, though the sodium sulphite is still added 
to the developer to ensure clean working and 
freedom from staining. It is also used as a pre- 
servative for most of the more recently intro- 
duced developing reagents. 


BICHROMATE 


The bichromates commonly referred to in photo- 
graphic literature are “‘ Potassium Bichromate”’ 
and “‘ Ammonium Bichromate”’ (which see). 


BICHROMATE DISEASE 


A skin disease that affects some workers who 
use potassium bichromate extensively. It occurs 
only when the skin is particularly sensitive and 
the hands are brought much into contact with 
the bichromate (dry or dissolved), and it takes 
the form of small ulcers or an irritating “‘ rash.” 
A preventive is to wear rubber gloves or finger- 
stalls. The hands should always be well washed 
in warm water after using bichromate, and wiped 
thoroughly dry. The use of a carbolic soap will 
often give relief from the itching, the hands 
being afterwards rubbed with a cooling oint- 
ment or the following mixture: Glycerine 
4 drms., carbolic acid 1 drm., alcohol 5 oz. For 
very severe cases the following treatment has 
been advised: Rub into the skin a little nitrate 
of mercury ointment (obtainable from most 
chemists, and called by the Pharmacopceia 
**Unguentum hydrargyri nitratis’’). (See also 
** Skin, Effects of Chemicals Upon.’’) 


BICHROMATE LAMP 


A lamp for dark-room use in which a solution 
of potassium bichromate serves as the light 
filter. Howard Farmer found that the various 
kinds of ruby and orange fabrics and glass in 
common use transmit only 2 per cent. or less 
of the light, whereas a 6 per cent. solution of 
potassium bichromate gives quite as much 
safety and gives more than 80 times the 
amount of illumination possible with orange 
glass. With other solutions the differences are 
still greater, but the potassium bichromate 
solution appears to be the best for general use. 
Most bichromate lamps are based on the pattern 
designed by Farmer, whose original lamp is 
shown at A. It consists of two concentric 
glass cylinders, about 4 in. and 5 in. in diameter 
respectively, placed one inside the other, mounted 
on a suitable solid base and furnished with a 
wooden cap, in which is mounted an incandes- 
cent electric bulb. This is excellent as a central 
light. A glass tank, for use with oil or gas lamps, 
is shown at B and C, such tanks being filled 
with a suitable solution and used in place of the 
usual red glass. As either type of lamp may be 
filled with any light-filtering solution, an oppor- 
tunity is afforded of adapting the actinic quality 
of the light to particular requirements. A 6 per 
cent, solution of potassium bichromate is safe 


61 


Bicycle 


for bromide papers, but not for dry plates, 
especially isochromatic plates, a safe solution 
for which is made as follows: Dissolve 1 oz. of 
the bichromate in about 9 oz. of water. Take 
about 4 oz. of the solution, and add 1 drm. of 


A. Bichromate 
Lamp 


B. Tank Light 
Filter 


C. Section 
of Tank 
Light Filter 


eosine, which is a strong red dye, and gently 
heat until the colour is a deep red ; mix the two 
solutions and pour into the lamp cell. Should 
the solution have a muddy appearance, pass it 
through filter paper. 


BICHROMATE REDUCER 


An acid solution of potassium bichromate 
may be used as a reducer for dense negatives 
in the same way as the more popular acid solution 
of potassium permanganate. A suitable formula 
1s :— 


Potassium bichromate 200 grs. 20 g. 
Sulphuric acid 4 oz. I°2 ccs. 
Water to 28 dees 1,000 ,, 


Dissolve the bichromate in water, and add the 
acid. The solution keeps well, but is liable to 
be irregular in action. 


BICHROMATED GELATINE 


A term fully explained under the heading 
“Carbon Process,’’ It refers to gelatine that 
has been sensitised with potassium bichromate. 


BICONCAVE LENS 


A lens, either simple or compound, of which both 
outer surfaces are concave. (See also ‘‘ Lens.’’) 


Biconcave Lens Biconvex Lens 


BICONVEX LENS 
A lens, either simple or compound, of which 
both outer surfaces are convex. (See also “* Lens.’’} 


BICYCLE (See “‘ Cycle.’’) 


Bi-gum Process 


BI-GUM PROCESS 
A familiar designation for the ‘‘ Gum-bichro- 
mate Process”’ (which see). 


BINDERS 


For lantern’slides and transparencies, binders 
consist of narrow strips of gummed paper by 
means of which the plate bearing the image is 
secured to the plain glass which is placed over 
the film as a protection. They are made in two 
forms, short lengths sufficiently long for one edge 
of the lantern slide only, so that four binding 
strips are required for each slide, and long strips 
sufficiently long to bind all the four edges with 
one piece. The former are very much more 
easily applied. 


BINOCULAR 


Photographically, this is another name for 
““ stereoscopic” (which see). 


BINOCULAR MICROSCOPE 
scope.’’) 


BIOGRAPH 


A kinematographic instrument invented by 
Herman Casler, of Canastota, New York, U.S.A. 
In the early stages of kinematograph science the 
size of the film pictures was (as now) only 1 in. 
by ¢ in., and owing to optical and chemical 
limitations early results were unsatisfactory. 
Casler considered that improvements could be 
made if the film pictures were taken on a larger 
scale ; and he proceeded to devise the biograph, 
in which he arranged to take pictures measuring 
23 in. by 27% in. and to utilise the whole surface 
of the film, dispensing with side perforations, by 
the introduction of an arrangemert of rollers, 
instead of sprocket wheels. Hence he presented 
his invention to the public in America during 
the autumn of 1896, The biograph projected 
pictures at the rate of thirty to forty per second, 
and flickering was thus largely overcome. 
Further, Casler, claimed that inasmuch as the 
film was carried forward by friction rollers 
instead of by sprocket teeth, there was greater 
steadiness of the images upon the screen, Against 
the advantages indicated must, however, be set 
the increased cost of production and the incon- 
venience of cumbersomeness in both the taking 
apparatus and the projecting machines. The 
biograph enjoyed a season of popularity in the 
United States and also in London; but it 
failed to become universal, whilst time has 
shown that small-size pictures and simpler appar- 
atus could be improved to meet all requirements. 


BIOSCOPE 


A well-known type of kinematograph projector. 
The name is derived from two words signifying 
respectively life and to see, and was in use long 
before the introduction of the kinematograph, to 
which it was first applied by Charles Urban, at 
that time associated with the Warwick Company. 
The courts did not sustain the use of the word 
as a trade-mark, 


BIRDS, PHOTOGRAPHY OF 

Most of the methods used in the photography 
of animals (see ‘ Animals, Photography of,’ 
“ Zoological Photography,” etc.) apply also in 


(See * Micro- 


62 


Black Line Process 


the case of birds. There are other points, how- 
ever, to be taken into account. Many birds are 
not only small in size, but are difficult to pil pach 
because of their natural timidity and wildness, 
this being especially the case with birds in a 
free state. The telephoto lens becomes of in- 
creased value, even high magnifications having 
often to be employed. Even more than in the 
case of animals, it is necessary to possess con- 
siderable knowledge of the haunts and habits of 
birds, and frequently there must be added an 
unbounded store of patience and perseverance. 
It is frequently necessary to use all sorts of 
elaborate and ingenious appliances to bring the 
camera into workable proximity to the bird 
without alarming it and arousing its suspicions. 
In fact, no work of much value can be done in 
the direction of bird photography without making 
a special study of it and acquiring the necessary 
knowledge and apparatus to make good results 
possible, Particular attention should be paid 
to effective and characteristic pose, and natural 
surroundings, and the use of orthochromatic 
plates and suitable screens is often imperative 
to secure a true rendering of the colour values 
of the plumage. 


BIS-TELAR 

A telephoto lens of fixed magnification, intro- 
duced by Busch. It has a focal length of about 
1} times the camera extension required, and the 
two kinds obtainable work at f/9 and f/7 respec- 
tively. Itis well adapted for hand-camera work, 
and is largely used by press photographers when 
photographing distant objects. 


BISULPHITELYE (See “ Sodium Bisulphite.’’) 
BITUMEN (See ‘ Asphaltum.”’) 

BITUMEN OF JUDEA (See “ Asphaltum.’’) 
BLACK CLOTH (See “ Focusing Cloth.”) 


BLACK, DEAD 


Recipes for dead blacks are given under the 
heading ‘‘ Blackening Apparatus.” 


BLACK LINE PROCESS 


A name given to the original ferro-gallic, or 
Colas process, described under the heading 
** Ferro-gallic Process.”’ 

Another process known as “black line” is 
a printing process worked out in 1894 by R. 
Nakahara, of Tokyo. The sensitising solution 


is :-— 
Gum arabic . “ 9, OZ. 93 g 
Water . . < Tae 625 ccs 
Tartaric acid . 192 gts 12.4.5 
Common salt 864. Gace 
Ferric sulphate 2 OZ. a ae 
Ferric perchloride. 3 ,, OF aa 


The gum is dissolved by heat in the water, and 
the other chemicals added to the warm solution. 
The solution is spread over well-sized paper 
with a sponge, and, after allowing it a little time 
to penetrate, all superfluous moisture is removed 
with the sponge well wrung out, and the paper 
dried as rapidly as possible. The exposure to 
daylight under a negative or plan is rather long. 
The colour of the prepared paper is yellow, but 


Black Mirror 


during printing all but the lines turn to white. 
The print is developed in a plain aqueous solu- 
tion of gallic acid, the strength of which is not 
important ; the print must not be left too long 
in the developer or stains will result. The 
developed print is rapidly washed and dried. 
Success depends chiefly upon the sponging off 
of the superfluous sensitising solution and rapid 


drying. 


BLACK MIRROR 
A mirror formed of black glass and used for 
photographing clouds by reflection 


BLACK OXIDE OF MANGANESE (See 
** Manganese.’’) 


BLACK, PROCESS 

A black water-colour pigment largely used in 
retouching photographic prints with the aero- 
gtaph and otherwise for process reproduction. 
It is claimed that it has no blue in its com- 
position. It may be diluted with water for pure 
greys, or mixed with Albanine for the lighter 
shadows. It dries a dull black and reproduces 
well, 


BLACK SPOTS 

Black specks on negatives and prints, but 
more patticularly upon ordinary P.O.P. Those 
upon the P.O.P. are caused (a) by metallic 
particles in the first washing water, these coming 
from a pump, tap, pipes, cistern, etc.; or (b) by 
trimming the untoned prints upon a metal plate. 
The spots cannot be removed, but they are 
easily prevented by immersing the prints before 
toning in a 10 per cent. solution of common 
salt, so as to convert all the soluble salts of silver 
into chloride, then washing again before toning. 
The addition of a little washing soda to the salt 
solution has also been recommended, the actual 
formula being 2 oz. of common salt and 1 oz. 
of washing soda to 1 pint of water. The prints 
are left in this for from five to ten minutes, then 
washed in running water for five minutes, and 
toned as usual. The above method serves to 
prevent spots, but when platinum is used as a 
toner instead of gold, the washing soda should 
not be used, only the plain salt and water. 

Black specks upon negatives and developed 
prints (bromide and gaslight papers) are caused 
by undissolved particles of the developer proper, 
hydroquinone, amidol, etc., settling upon the 
film. These particles may be present undis- 
solved in a freshly made developer, or may be 
flying about the room and settling upon the 
sensitive surface in the form of dust. 


BLACK TONES 

Black tones are obtainable upon carbon and 
other pigment papers, which already have a base 
of black pigment, platinotype, bromide, and gas- 
light papers with ease, and on print-out papers 
with difficulty. The richness and quality of the 
blacks on platinotype are characteristic of the 
process and depend upon the state of the paper, 
exposure, etc. The quality of the blacks upon 
bromide and gaslight papers depends upon the 
exactness of exposure and upon the state of the 
developer, because if too much potassium 
bromide is used in the latter the blacks are 


63 


Blackening Apparatus 


greenish in tone, and if too little is used neither 
the blacks nor the whites are of the best. 

All tones upon P.O.P. largely depend upon the 
quality of the negative; and for black tones the 
negative should preferably be rather hard—that 
is, should have dense high lights and clear 
shadows. Such a negative should be printed 
under green glass and toned in any gold or 
platinum bath, or in the following combined 
toning and fixing bath:— A. “Hypo” 4 oz.; 
water 10 oz. B. Lead nitrate 1 oz.; distilled 
water 10 oz. ; glacial acetic acid 48 drops. Add 
B to A gradually, and with shaking, until a 
distinct cloudiness appears; then filter, Take 
Io oz. of the above mixture and add 1 grain of 
gold chloride, and this forms the toning bath. 
If black tones do not result, the negative was 
not suitable, or the printing has not been suit- 
ably carried out. Some workers obtain a rich 
black tone on P.O.P. by using gold first and 
platinum afterwards, but, as in all cases, much 
depends upon the suitability of the negative. 


BLACK VARNISH (See “ Varnish.’’) 


BLACK VIGNETTES 


A style of portrait known also as “ Magic,” 
“‘ Egyptian,” and “‘ Russian ” vignettes, invented 
in 1868 by a Russian photographer named 
Bergamaso, The sitter’s head is made to stand 
out against a perfectly black background, the 
edges of the picture all round being black 
instead of white as in an ordinary vignetted 


A. Black Vignetting 
with Serrated Card 
in front of Lens 


B. Black Vignetting 
with Card inside the 
Camera 


portrait. The sitter is placed against a per- 
fectly black background, and the light is pre- 
vented from acting on the edges of the plate, 
more particularly on the lower part (upper part 
as it is seen on the focusing screen). The light is 
cut off from the plate either by means of a ser- 
rated piece of blackened card or tinplate on an 
adjustable rod outside the camera, and before 
the lens, as A, or by the insertion of a black card 
with an opening in the centre, in the bellows 
of the camera, as B. Either system, when 
properly used, cuts off the light at the top or 
bottom and gives a negative with plain glass 
borders which print black, the well-lighted head 
appearing in the centre. 


BLACKENING APPARATUS 

Only a dead black is suitable for the interior 
of a camera, as a glossy black would give rise 
to reflections. 

Blackings should be tested upon pieces of 
metal, wood, leather, etc., before applying to 
the apparatus. Recipes are as follow: 


Blacklead 


Brasswork.—To blacken camera brasswork, 
clean with fine emery, rinse, and immerse in a 
saturated solution of copper nitrate for about 
two minutes. Then take out, heat over a 
Bunsen burner or ordinary spirit flame, and 
repeat the process several times. To make the 
copper nitrate, dissolve 1 oz. of copper filings in 
2 oz. of nitric acid; do this in the open air, and 
stir with a glass rod to assist dissolving. 

Zincwork.—Clean and rinse as before, and 
immerse in a solution of copper chloride 45 grs., 
zinc nitrate 30 grs., and water 4 oz., to which is 
added 4 oz. of hydrochloric acid. Finally, rinse 
and dry. 

Tin.—Use carbon black mixed with the least 
possible amount of French polish. Excess of 
polish makes it glossy. A dye can be used instead 
of a pigment; for example, boil together 1 oz. 
of water, 15 grs. of borax, 30 grs. of shellac, and 
15 minims of glycerine. Maintain the boiling 
till dissolved, and then add 60 grs. of nigrosin. 

Bellows Interiors.—Use a solution of shellac 
in methylated spirit coloured with lampblack. 

Camera Interior (Woodwork).—Dissolve }4 oz. 
of shellac and } oz. of borax in 10 oz. of hot 
water, and add about } drm. of glycerine and 
sufficient aniline black (soluble in water) to form 
a good solid black. Two coats should produce 
a rich velvety dead black. Another recipe is: 
Aniline black 50 grs., gum shellac 100 grs., 
methylated spirit 2} oz. Negative varnish 
mixed with powdered lampblack may also be 
used. 

Lampblack mixed with gold size and turpentine 
makes a good dead black for general use. 


BLACKLEAD (Fr., Plombagine ; Ger., Graphit) 


Synonyms, graphite, plumbago. Used for 
lubricating apparatus and in retouching. 

In process work, finely powdered blacklead 
is sometimes rubbed on to wet plate half-tone 
negatives in order to intensify the dots in certain 
parts where additional density is required. It 
is also used in the ‘‘ Powder Process” or 
“Dusting-on Process”? for the duplication of 
negatives. As an inert powder it forms an acid 
resist, and is dusted-on to an ink image for that 
purpose. In electrotyping it is used to give the 
wax mould an electro-conductive surface. 


BLAKE-SMITH PROCESS 

The modern method of toning bromide prints 
by first bleaching the image or converting it 
into such a form that treating with a sulphide 
solution will convert it into sulphide of silver; 
largely due to the experimental work of R. E. 
Blake-Smith. Various methods of bleaching 
the image have been used, but the most simple 
as well as the most satisfactory is to convert 
the image into a bromide or chloride by means 
of a solution containing potassium ferricyanide 
and either potassium chloride or potassium 
bromide. (For details of this method, see “’Ton- 
ing Bromide Prints,” etc.) 


BLANC D’ARGENT 


A pure white pigment water-colour of French 
manufacture, largely used by process retouchers, 
and preferred for aerograph work. Drawings or 
retouching done with it should be reproduced 
without delay, as it discolours. 


64 


Blisters 


BLANC FIXE (See “ Barium Sulphate.’’) 


BLANCHARD, VALENTINE 


Born at Wisbech, 1831 ; died at Herne Common, 
November 14, 1901. A famous portrait photo- 
gtapher in the sixties and the inventor of appar- 
atus and processes. He was the first to recommend 
making large transparencies from small negatives, 
and the art of printing-in clouds from separate 
negatives, the latter being published on Septem- 
ber 4, 1863. He was always opposed to micro- 
scopic sharpness in definition, and the slight 
diffusion which he gained by the use of a single 
lens caused much attention to be paid his work. 
He was an advocate of long exposures and large 
plates, giving about forty-five seconds’ exposure 
and using 15-in. by 12-in. plates for his por- 
traits. His method of obtaining carbon prints 
without transfer consists in immersing the 
tissue for a minute in petroleum, the paper sup- 
port being thus rendered translucent. The 
tissue, after the removal of the surplus oil, was 
placed in a printing frame with the support next 
the negative, printed in the usual manner, and 
developed from the front. He also invented a 
brush, known as the Blanchard brush (see 
‘‘ Brushes’’), which is widely used for sensitising. 


BLEACHING NEGATIVES (See “Intensi- 
fication.’’) 


BLEACHING POWDER (See “Calcium 
Hypochlorite.’’) 
BLEACHING PRINTS (See ‘* Drawings 


Made from Photographs.’’) 
BLIND SHUTTER (See “ Shutters.’’) 
BLINDS, STUDIO (See “ Studio.’”) 


BLISTERS 


Blisters appear at times upon all makes of 
plates, films, and papers in the manufacture of 
which albumen or gelatine is employed, but 
the papers most subject to the trouble are 
albumen and bromide. The principal cause of 
blisters is the use of a too strong ‘‘ hypo” bath, 
rapid washing, excess of alkali in the developer, 
and the difference in temperature between the 
developing, toning, or fixing solutions and the 
washing water. The blisters usually appear 
when the plates or papers are being washed after 
fixing. It is a curious fact that fewer blisters 
appear where ordinary tap water is used than 
where soft water is employed. It is, however, 
the fixing bath that usually needs attention when 
bromide and gaslight papers are prone to blister, 
The fixing bath, as freshly made with cold water 
and “‘ hypo,” should not be used immediately, the 
temperature of such a solution dropping almost 
to freezing point, and of course many degrees 
lower than the temperature of the washing water 
used before and after; hence the expansion of 
the wet gelatine, which is very susceptible to 
temperature, in the form of blisters. If a fixing 
bath is needed quickly it should be made with 
hot water and used when the temperature has 
fallen to the level of the washing water; or, 
if cold water is used, the bath should be mixed 
some considerable time before use in order that 


AHdVUYDOLOHd TVOIDO'TOOZ 


AY) 


Blisters 


it may have time to rise in temperature. When 
care is not taken about the temperature of the 
bath, blisters may be prevented by allowing the 
washing water to run gradually into the fixing 
bath while the fixed prints remain therein. The 
water gradually replaces the “‘ hypo,” the differ- 
ence in temperature (if any) is gradually made up, 
and the expansion of the gelatine is too slow to 
do any harm ; this method, too, largely prevents 
blisters due to the use of a strong fixing 
bath. 

The use of an acid fixing bath is widely advo- 
cated for the prevention of blisters on bromide 
papers and negatives. Any formula will serve, 
but that containing “hypo” and metabisulphite 
will be found best. Another plan is to soak 
the prints previous to, or immediately after, 
fixing in a 20 per cent. solution of formaline 
and then to wash well. There is really no satis- 
factory cure for blisters when once they have 
appeared ; pricking the paper at the back with 
a pin for the purpose of allowing the air to 
escape from the bubble has been advised, but 
the loosened film mever becomes properly 
attached to the paper, and frequently peels off 
when dry. Another plan is to squeegee the 
blistered print upon cleaned ground glass and 
strip when dry, but, as in the previous remedy, 
the blisters invariably scale off later. 

Information given above on preventing blisters 
applies equally well to negatives and bromide and 
gaslight papers. Blisters but rarely appear on 
negatives, but when they do the negatives 
should be soaked in methylated spirit and 
dried; a more general trouble with plates is 
““frilling ’’ (which see). 

Albumen paper, as a tule, blisters very badly 
if carelessly manipulated, the cause being the 
unequal temperatures of the solutions employed. 
Rives paper, which is now almost universal, 
is thought to blister more than the Saxe paper, 
which is tougher, but not now so widely used. 
Preventive measures are (a) to use solutions 
of as even temperatures as possible; (b) to soak 
the prints in hot water or methylated spirit, 
afterwards washing well, previous to toning ; 
(c) to remove the prints from the ordinary alka- 
line fixing bath (acid baths must not be used 
for albumen paper) te water to which has been 
added one-tenth its weight of common salt, 
allowing them to remain for ten minutes and 
finally washing well. . 

Carbon trints show minute blisters when the 
water used is too hot. Blisters may be also due 
to free air in the water, greater trouble in this 
direction being experienced when water comes 
direct from the main than when it comes through 
a cistern. It is advisable to boil sufficient water 
for the bath in which the tissue is to be soaked 
before squeegeeing to the temporary or final 
support. Fifteen minutes’ boiling should be 
sufficient to expel all the air, and it is then cooled 
in a jug in order that only a small surface may 
be exposed to the air, of which water can absorb 
a large quantity. 

Gelatine (P.O.P.) prints rarely blister, but when 
they do the cause is a too strong “‘ hypo ’”’ fixing 
bath, or the unequal temperatures of solutions 
and water. An acid fixing bath must not be 
used for P.O.P.; if hardening is thought 
necessary, formaline should be used. 

5 


65 


Blocking Out 


BLITZ-PULVER 


The German name for flashlight powder. It 
is occasionally used in English and American 
literature. In the United States, a powder having 
this name contains the mixed nitrates of barium 
and strontium 5 oz., metallic magnesium 2 oz., 
and amorphous phosphorus 120 to 180 grs. 


BLOCK (Fr., Cliché, Planche; Ger., Block, Auto- 
typie-druckform, Autotypiehlischee, Galvano) 
A block of wood or metal, or metal plate 
backed by either wood or metal, and having a 
typographic printing surface. It may be a pro: 
cess block (produced photographically), a wood- 
cut, in the production of which photography 
may or may not play a part, an electrotype, or 
stereotype. “Block Processes” include ll 
those processes in which, by the aid of photo- 
gtaphy, a relief surface is produced, capable of 
being printed from in an ordinary printing press 
together with letterpress. 


BLOCKING OUT, OR STOPPING OUT 
A method of painting out undesirable details 
upon a negative, the painted portions appearing 
white upon the finished print; parts of lantern 
slides may also be blocked out, in which case 
the blocking out appears black upon the screen. 
Blocking out is extensively used on photographs 
of machinery, furniture, etc., for reproduction in 
catalogues, etc. It is generally desired that the 
article photographed should stand by itself upon 
a white ground, in which case opaque pigment is 
used as the medium for stopping out the rest of 
the picture; but when a perfectly black back- 
ground is required the best thing to do is to 
make a transparency and block this out, and 
from this to make a second negative, on which 
the blocked-out portions will be clear glass, 
which will, of course, print black. Whichever 
method is adopted, the actual work of blocking 
out is precisely the same. In order to do the 
work properly, the following materials are 
necessary: a retouching desk, one or two sable 
or crow-quill brushes with fine points, a mapping 
pen, Indian ink, ruler, a bottle of black varnish, 
and red water-colour or other opaque medium. 
The negative is placed film side uppermost on 
the retouching desk and the film worked on with 
the opaque. A rough print to serve as a guide 
should be taken from the negative before the 
work of blocking out is begun. It is advisable 
also to begin from the centre of the negative 
and work outwards. A retoucher with a steady 
hand may be able to do all the necessary work 
with a brush, but many will need the rule, pen 
aud ink. The pen, if used, is charged with 
Indian ink and held perfectly vertical to the sur- 
face of the plate; it should have a smooth and 
well-rounded point, as otherwise it is apt to cut 
the film. Any errors made with the pen and 
ink may be removed by washing away the line 
by means of a camel-hair brush charged with 
water; but when this is done care must be taken 
to wait until the gelatine film is perfectly dry 
before going over it again with a pen, otherwise 
the film will be torn. Having ruled all the 
necessary lines, the rest of the blocking out may 
be done with the black varnish diluted with 
turpentine, or with any other opaque pigment. 
Those pigments used with water are perhaps 


Blood Albumen 


the easiest to use because, should any error be 
made in the work, they may easily be washed 
off, or wiped off with a damp sponge, whereas 
black varnish is difficult to remove even with tur- 
pentine; the varnish, however, is the more durable, 
and will stand any amount of wear and tear. 

All the fine work, if desired, may be done on 
the film side with a pen and Indian ink, or with 
a brush charged with opaque or red water-colour, 
and the bulk of the stopping out on the glass 
side with black varnish or Brunswick black, 
taking care that the working on one side over- 
laps the other. 

Another method is to take a rough print from 
the unblocked negative, cut out the part required, 
and use the cut print as a mask, which may be 
pasted on the glass side of the negative. This 
serves as opaque, and but little fine work may 
be required on the film side, care, however, being 
taken to let the working on the film side overlap 
the paper mask. The latter may, if desired, be 
wetted and placed on the film side, but it is 
removed more easily from the glass side of the 
negative. (See also ‘‘ Camphor.’’) 

Any of the above methods may also be 
employed for transparency work, but in the case 
of lantern slides it will be mecessary to use a 
stopping-out mixture which will not crack when 
subjected to the heat of the lantern illuminant 
concentrated by the condenser. 

The present-day commiercial practice is for 
the photographer to make as good a photograph 
of the subject as he can, supply a good print, 
and leave the blocking out to the process 
worker’s artist, the work being done on the 
print and not on the negative. The photo- 
gtapher can often assist matters by seeing that 
the background is of such a nature that the work 
of blocking out is facilitated, as the merging of 
the picture of a machine, for instance, into the 
background makes it difficult to see where one 
ends and the other begins. Frequently it is 
sufficient to run a line of white pigment between 
the subject and the background, and the process 
worker then understands that the latter is not 
to be included. The aerograph is largely used 
for blocking out on prints, etc. 


BLOOD ALBUMEN 


BLOTTING~PAPER 


Used for blotting off water from negatives, 
and for drying those papers not having a gelatine 
or sticky surface. Inked and coloured blotting- 
paper is not suitable. The paper should be as 
fluffless as possible; special blotting-papers for 
photographic purposes are obtainable. Ordinary 
blotting-paper may be freed from all impurities 
likely to damage prints by pouring boiling water 
and a hot weak solution of sodium carbonate over 
it alternatively two or three times, ending with 
the boiling water. This treatment removes the 
acids and sulphites, which might otherwise affect 
the permanency of the silver prints. 


BLOW-THROUGH JET (See “ Limelight.’’) 


BLUE GLASS, PHOTOGRAPHIC USES OF 

Blue glass of good quality has several uses 
in photography. By looking through a piece of 
it at the view to be taken, or by fixing a sheet 


(See ‘* Albumen.’’) 


Blue-Print Process 


of it over the focusing screen, the photographer 
is enabled to see the subject with its colour con- 
trasts toned down, and will be the better able to 
judge what the effect will be in a photographic 
monochrome print. Some years ago blue glass 
was advocated for glazing studios, but exposures 
under blue glass need to be longer than under 
white glass, and the only gain to the photo- 
gtapher is that he is working in a light that is 
less trying to his eyes. Blue glass is of service 
if placed over a harsh negative when printing 
on P.O.P., it having the effect of giving a softer 
print, inasmuch as certain organic salts are not 
acted upon as they would be were the blue glass 
absent. Blue glass is also of service when copy- 
ing a faded or yellowish photograph; a piece of 
pale blue glass is held before the lens during the 
exposure, and the resultant negative gives 
increased contrasts, and in general is of better 
all-round quality. 


BLUE TONES 

These are obtained most easily on blue-print 
(ferro-prussiate) paper or by using blue carbon 
tissue, in both cases a blue print being produced. 
Good blues are difficult to obtain on P.O.P., a 
blue-black (which see) being the nearest. Bromide 
prints may be partially or wholly changed to a 
prussian blue. Ferric ferricyanide is usually 
employed, it being made as required by mixing 
together solutions of potassium ferricyanide and 
ferric ammonium citrate, adding a little nitric 
acid. The formula for the toner is :— 


Potassium ferricyanide 45 grs. 10g. 
Nitric acid (pure) . 24 mins. 5 ccs, 
Ferric ammonium citrate 22 grs. 5 g. 


Water . 


If this works too quickly, add more water. Place 
the prints, after developing, fixing, and washing, 
in the above, until of the desired colour, and 
wash in running water for twenty minutes, or 
until the whites are clear. 


BLUE VITRIOL (See “‘ Copper Sulphate.”) 


BLUE-BLACK TONES 


In silver printing these can be obtained only 
by using a toning bath rich in gold, say I gr. to 
5 oz. or 6 oz., and also a liberal allowance for 
the prints being toned, 2 grs. or more to each 
full-size sheet of paper, or fifteen half-plate 
ptints. In addition, a rich print from a strong 
negative is absolutely essential, the tone of the 
shadows being very largely determined by their 
depth. Some toning baths will give blue-black 
tones much more readily than others; with 
some, these tones cannot be obtained. In 
separate toning and fixing the sulphocyanide 
bath, if strong, will give blue-black tones readily. 
In combined toning and fixing Bennett’s toning 
bath will give a similar result by increasing the 
quantities of the B, C, and D solutions. One and 
a half drams of each should be used to each 
ounce of the A solution, in place of 1 drm., as 
given under the heading ‘‘ Bennett’s Toning 
Bath for P.O.P.” 


BLUE-PRINT PROCESS 
Known also as “ Cyanotype”’ (negative) and 
“ Ferro-prussiate ’ process, and largely used by 


IO OZ. 1,000 ccs, 


Blue-Print Process 


engineers, architects, etc., for reproducing 
technical drawings. It is one of the oldest 
photographic printing processes, having been 
invented by Sir John Herschel in 1840. Paper 
is coated with a mixture of ammonio-citrate of 
iron and potassium ferricyanide dissolved in 
water, then dried in the dark, and printed by 
daylight in contact with a negative or drawing 
on tracing paper, when an image in insoluble 
Prussian blue (Turnbull’s blue) is produced. The 
print is washed to remove the soluble coating 
unacted upon by light, leaving a finished print, 
blue on a white ground. 

Another blue-print process is the positive 
cyanotype, or Pellet’s process (which see, under 
the latter heading), which gives blue lines on a 
white ground, the opposite process to the above, 
it being one in which blue is formed where the 
light does not act. The negative cyanotype or 
blue-print process proper is the one particularly 
suitable for negatives, and is that to which 
attention is here directed. 

Blue-print paper, ready sensitised for imme- 
diate use, may be purchased, but as it does not 
keep well, and is so easy to prepare, it is better 
to make it as required. A large number of 
sensitising formule have been published from 
time to time, considerable latitude being per- 
missible in the quantities of chemicals used as 
well as in the methods of working. They all, 
however, resemble one another, and yield prints 
which are all very much alike. Almost any kind 
of paper can be coated with the sensitive mix- 
ture; fairly stout cream-laid notepaper, or a 
real photographic paper such as Rives, is as 
good as any; it should be free from wood-pulp 
or other impurities usually found in cheap white 
papers, its surface should be fairly hard and not 
too absorbent, and it should be tough enough to 
withstand thorough washing. Common rough 
papers are better if sized before sensitising, 
because the size prevents the image from sinking 
into the paper. For the size use the following 
arrowroot mixture :—Take 4 oz. of arrowroot 
and mix to a smooth stiff paste with a small 
quantity of cold water. Add warm water to 
make 22 oz. in all, and boil gently until clear. 
Thin papers may be immersed bodily in the 
warm mixture for a minute or two, and then 
drained and dried. Thick papers should be 
pinned by the corners to a flat board and the 
warm size applied first up and down and then 
across, by means of a soft sponge or a Blanchard 
brush (see the heading ‘‘ Brushes”’). Then witha 
clean soft sponge go over the paper again in order 
to efface all streaks and make the surface smooth ; 
hang up, and when quite dry it is ready to sensi- 
tise. The two sensitising solutions are made 
according to the following formule :— 


A. Ferric ammonium 
citrate (brown) . 80 grs. 160 g. 
Water. I OZ. 1,000 ccs, 
B. Potassium ferri- 
cyanide . 60 grs. 120 g. 
Water . ion. ih: ORs 1,000 ccs. 


Unless quite fresh and clear the ferricyanide 
crystals should be washed before weighing, and 
dried between blotting-paper, to free the crystals 
from powder or crust. Mix the solutions, and 
keep in a stone bottle or in a dark place. The 


67 


Blue-Print Process 


solution is usable at once, but works better 
when a week or ten days old, but it must be 
filtered just before using, and if older than this, 
should be preserved by adding to every 2 oz. 
of it 1 gr. of potassium bichromate. The sized 
common paper or the plain good paper, with 
blotting-paper underneath it, should be pinned 
to a flat board, placed (as illustrated) at an 
angle of about 20° to the horizontal in pre- 
ference to being either flat or upright. Suff- 
cient of the sensitive solution should be poured 
into a saucer and then applied to the paper 
with a sponge, Buckle brush, or large soft camel- 
hairmop. The coating must be done in artificial 
light or very weak daylight, and the solution 
should be spread upon the paper by strokes 
across the sheet, beginning at the top and joining 
the second stroke to the first. The strokes 
should then be made vertically in order that the 
paper may receive a perfectly even coat, without 
any of the sensitive mixture running in rivulets 
down the sheet. When evenly coated the paper 
must be dried as quickly as possible, and in the 
dark—a warm cupboard is a good place—but no 
very great heat should be applied to the wet 
paper to hasten the drying. The coated paper 


Paper Ready for Coating in Blue-print Process 


will not keep good for many days; a heavily- 
coated poor paper will not keep so long as an 
unsized or lightly sized good one. The colour 
of the sensitised paper may be a dirty greenish © 
yellow tinge, but will vary according to the 
sensitising formula. The paper is placed in 
contact with a negative or drawing on tracing 
paper, and printed by daylight, preferably in 
strong sunlight. On exposure to light the colour 
of the paper gradually changes through bluish- 
green and bluish-grey to a kind of dirty olive- 
green, the image having a choked-up appearance 
when fully printed. The print is washed for 
about fifteen minutes in water, which should 
remove the soluble salts and leave a brilliant 
blue print. The water serves both as a developer 
and fixer, the print needing no further treat- 
ment. Prolonged washing weakens the image, 
as will also water containing carbonate of lime. 
Brighter prints are obtained by adding about 
20 gts. of citric acid to the pint of water. A 
solution of 5 parts of alcohol in 95 parts 
of water has been advocated for improving 
the whites, and a 2} per cent. alum solution has 
been recommended for brightening the blue 
colour; but neither of these aids is necessary if 
the water is free: from lime, the negative or 
tracing a suitable one, and the paper properly 
prepared. 


Blue-Print Process 


An alternative method is to use single solu- 
tions, one for sensitising and the other for 
developing the faint image, obtained by printing 
in the usual way, to the desired blue colour. 
The sensitising mixture is as follows :— 


Ferric ammon. citrate (green) IIo gts. 
Uranic nitrate 45 r 
Water I OZ. 1,000 CCS. 


Paper is coated with this mixture and printed 
in the manner already described. The faint 
image is developed to its full strength by placing 
in— 
Potassium ferricyanide 
Water. : 


The print is completed by washing in water. 
This process is more rapid than the one first 
described. 

The blue-print processes are used for printing 
upon fabrics and for the making of blue trans- 
parencies for window decoration. For the latter 
it is necessary to use a plate coated with gelatine 
to serve as a vehicle for the sensitiser. 

Toning Blue-prints.—Blue-prints may be 
toned to several other colours, but the various 
formule published are uncertain in their action on 
home-made papers, two samples of which are 
seldom alike; they answer better with com- 
mercial blue-print papers. Before toning, wash 
the prints thoroughly. Gveen.—Make a satur- 
ated solution of ferric protosulphate, acidify with 
sulphuric acid, and dilute with an equal quantity 
of water. Immerse the blue-print until the 
required tint is obtained, wash well, and dry. 
A weak solution of sulphuric acid (acid 4 drops, 
water 1 oz.) will also give the print a greenish 
tinge. Lilac.—For lilac-violet, immerse in a 
hot solution of lead acetate, or a cold solution 
of borax. A 2 per cent. solution of potassium 
sulphocyanide (10 grains in 1 oz. of water) gives 
a pink-lilac tone, after obtaining which blot off 
superfluous solution, expose to strong sunlight, 
wash, anddry. Greenish Black.—Dissolve 30 gts. 
of borax in 1 oz. of water and add sulphuric acid 
drop by drop till the solution just reddens 
litmus paper; next add a weak solution of 
ammonia till the red colour begins to change, 
and finally add 4 grs. of catechu, shake well and 
filter; tone, wash, and dry. Brownish Black.— 
Add 6 drops of liquor ammoniz to 1 oz. of water, 
immerse the blue-print, and allow to remain 
until the colour has vanished; then wash and 
place in water 1 oz., tannic acid 9 grs., in which 
the bleached print gradually assumes a brown 
or brownish black colour; wash and dry. 
Purple Brown.—Add 30 grs. of tannic acid and 
1 gt. of pyrogallic acid (or even less) to I oz. 
of hot water, immerse the blue-print until toned 
to a lilac, rinse, and place quickly into a weak 
solution of caustic potash (potash 8 grs., water 
I oz.); wash and dry. Black.—A good black is 
difficult to obtain; success depends upon the 
quality of the negative and upon the depth of 
the blue-print. The deep shadows tone to a 
rich black, but there is a falling-off in the half- 
tones. Of the many formule, Lagrange’s is the 
best, but one of the most troublesome. Rinse 
the print in distilled water and, in a yellow light, 
bleach in a silver nitrate solution (9 grs. in I oz. 
of distilled water). Wash well in distilled water, 


220 g. 
70 


3) 


22 grs. 
I Oz. 


44 g. 
I,OOO ccs, 


68 


Bolting Cloth 


expose to the fumes of ammonia, and afterwards 
develop with an ordinary ferrous oxalate de- 
veloper ; the print may then be washed and dried. 
Grey to Red.—Print darker than usual, wash 
for ten minutes, and immerse in a solution of 
copper nitrate (24 gts. to 1 oz, of water) to 
which a little liquor ammonie has been added 
cautiously, a few drops at a time, until the pre- 
cipitate first formed is just redissolved, leaving 
the liquid a deep blue. This bath turns the 
blue-print mauve, then grey, and after a time 
red. Prints dry more blue than they appear 
when wet. The bath does not act well on prints 
showing great contrasts, since by the time the 
dark parts have turned grey the half-tones and 
lighter tones will become red. Most of the tones 
obtained by the above methods are unsatisfactory. 
(See also ‘‘ Window Transparencies”’ and “‘ Fab- 
rics, Printing on.’’) 

Bleaching Blue-prints.—Instructions are given 
under ‘“‘ Drawings Made from Photographs.” 


BLURRING 


In a photographic image, the absence of sharp 
or crisp definition, a point of light becoming a 
nebulous circle, and a fine line a hazy broad 
band. Blurring may result from several inde- 
pendent causes. A large working aperture of 
the lens may be necessitated by the nature of 
the subject demanding a rapid exposure, and 
the difference in the various planes of the sub- 
ject may result in some being out of focus, and 
consequently blurred. Or occasionally, the 
entire image may be out of focus, either by 
accident or design, Many lenses, when used at 
full aperture, will not give sharp definition over 
the entire plate, and while the central part is 
crisp and well defined, the corners are blurred. 
Or the camera may move during the exposure, 
with the result that the whole image is blurred. 
Or, again, in photographing moving objects, the 
exposure may not be sufficiently short to pre- 
vent the object showing movement on the plate. 
A lens that has been tampered with and put 
together incorrectly, may give a blurred effect. 


BOLOMETER (Fr., Bolométre ; Ger., Bolometer) 

Practically an extremely sensitive thermo- 
meter formed of one, two, or four metallic grids 
or gratings so connected as to form a Wheat- 
stone bridge, and carrying a very sensitive 
galvanometer mirror. It is used to measure 
extremely small differences in temperature 
(o-oo00001° C.). S$. P. Langley utilised this instru- 
ment in conjunction with a series of rocksalt 
lenses and prisms, and received the deflected 
light from the galvanometer mirror on a strip 
of bromide paper. Thus he was able to meas- 
ure further into the infra-red and map out 
the absorption lines with remarkable accuracy. 


BOLTING CLOTH (Fr., Ger., 
Beuteltuch) 

A material of fine regular texture, originally 
made for bolting or sifting flour; known also as 
bolting silk and silk bolting cloth. It is used 
for obtaining softness of definition in a print. 
For use when enlarging upon bromide paper, a 
piece of the cloth, slightly larger than the enlarge- 
ment to be made, is stretched free from creases 
on a light wooden frame. This is interposed 


Etamine ; 


Bolton, W, B. 


between the enlarging lantern and the sensitive 
paper. It may be tacked over and in actual 
contact with the paper, but in this case the grain 
of the fabric shows as a canvas effect in the en- 
largement; it is more often used away from the 
paper, the greater the distance the greater being 
the diffusion obtained and the less marked being 
the grain. Different effects are obtainable by 
moving the bolting cloth during exposure, also 
by giving part of the exposure with the cloth 
and the remainder without. The interposition 
of the cloth increases the exposure by about 
one-third, but this largely depends upon the 
effect desired. 

In contact printing, the bolting cloth is placed 
in between the negative and the printing paper. 

The cloth may be obtained in various degrees 
of texture and in sheets up to 39 in. by 36in. It 
must be carefully handled, as it is easily dam- 
aged, and any tear shows upon the finished print. 
In the hands of an artistic worker bolting cloth 
is a useful device for obtaining soft pictures. 


BOLTON, W. B. 

Born 1848; died 1899. Editor of the British 
Journal of Photography from 1879 to 1885. An 
authority on photographic emulsions ; published 
in September, 1864 (with B. J. Sayce), a formula 
for collodio-bromide emulsion, and in January, 
1874, particulars of a washed collodion emulsion 
process, this amounting to an almost revolu- 
tionary improvement on the unwashed collodion 
process. 


BONE BLACK (Fr., 
Knochenfohle) 

The product formed in the retort by heating 
bones in the absence of air; animal charcoal. 
It contains about 10 per cent. of carbon and 
about 80 per cent. of calcium phosphate, the 
remainder being calcium carbonate and other 
substances. Used in photography as a pigment in 
carbon and like processes, also in plate backings 
and black varnish. Ivory black prepared from 
ivory chips is a similar but superior pigment. 


BOOK CAMERA (Fr., 
Ger., Buchkamera) 


An early form of detective camera, made to 


Noty animal; Ger., 


Chambre a livre ; 


Book Camera 


tesemble either a book, as shown, or several 
books strapped together. 


69 


Borders, Fancy 


BOOKS OF KINEMATOGRAPH PICTURES 
(See “‘ Kinematograph Pictures in Book 
Form.’’) 


BORACIC ACID 
Another name for boric acid (which see). 


BORAX (Fr. and Ger., Borax) 

The common name for sodium borate (which 
see). Also known as sodium biborate or pyro- 
borate. 


BORAX TONING 

A certain and reliable method of toning sensi- 
tised albumenised paper and some forms of 
plain salted paper prepared and sensitised by 
the worker. It is not very satisfactory as a 
toning bath for gelatino-chloride of silver emul- 
sion papers that is, for the modern printing-out 


paper. A good formula is :— 
Borax. : 80 grs. 248 
Gold chloride . ih a pO 
Water 8 oz. 1,000 ccs, 


The borax should be dissolved in boiling water, 
and when the solution is cool the gold should be 
added. The prints must be washed well before 
toning, and when the desired tone is obtained 
they should be rinsed in two or three changes 
of water and then fixed in the usual manner. 


BORDER PRINTING 

This is an alternative to mounting a print. 
A sheet of paper and a printing frame, both 
larger than the actual picture, are used, and 
by masking the negative the print appears in 
its first stage with a plain margin. Masks are 
next used to cover the picture itself, and also 
the plain margin with the exception of an edge 
all round the print. A second exposure then 
gives a narrow border to the picture. This 
method may be elaborated almost indefinitely, 
and ‘special printing frames are made to mini- 
mise the difficulty of securing accurate regis- 
tration. Used with discretion and taste, good 
effects may be secured by surrounding borders 
of varying width and tint, the great advantage 
being that the tone and quality of the tints are 
the same as in the picture itself. The great pit- 
fall is over-elaboration, resulting in distracting 
attention from the picture itself. (See “ Borders, 
Fancy.’’) 


BORDERS, FANCY 

These are generally made by means of special 
negatives (films, as a rule), which may he bought 
commercially in considerable variety. The sub- 
ject is first printed while the margin is masked 
and then the border printed while the picture 
is masked (see ‘‘ Border Printing’’). Some of 
the more tasteful of these borders are effective 
in making picture postcards, cards with Christ- 
mas greetings, and so on, When a small sub- 
ject is used, on a postcard, for example, a well 
printed border of good design and tone is pre- 
ferable to a bare expanse of white. At the same 
time, however, a picture of real value will prac- 
tically never gain in effectiveness by such an 
addition, and the suitability or otherwise of a 
fancy border for the purpose in hand needs 
careful consideration. 


Boric Acid 


BORIC ACID 
Borsdaure) 


Synonym, boracic acid. H;BO;. Molecular 
weight, 62. Occurs in shining scales or amor- 
phous powder. It is used in pyro developers 
as a restrainer and to prevent stains, and also 
in the fixing bath as a stain preventer. A solu- 
tion of 30 grs. of the acid in 1 oz. of water has 
been recommended for stopping development 
instantly. In cases of very great over-exposure 
it works well as a restrainer, the proportions being 
3 drops of a saturated solution added to each 
working ounce of developer. A formula for a 
pyro-hydroquinone developer containing boric 
acid is given under the heading “ Developers, 
Mixed.” As a preservative, 10 grs. may be 
added to each pint of developer, and it will 
then also act as a restrainer. In a fixing bath 
it may be added in the proportion of 70 grs. 
to each ounce of dry “‘ hypo” used, but should 
not be used after an acid developer. It was at 
one time recommended as an addition to the 
combined toning and fixing bath, but it is next 
to useless employed in that way, and may 
possibly harm the prints. However, Eder recom- 
mends its addition to the “hypo” bath when 
used before toning. (See “ Toning after Fixing.’’) 


BOTTLES (Fr., Ger., 
Flaschen) 

Narrow-mouthed bottles A are best for liquids, 
and wide-mouthed ones, B and C, for solids. 
Those with flat-topped stoppers are preferable, 
it being then less easy for dust to collect in the 
space between the neck and the stopper. A 
useful and neat type of bottle has a space for a 
label ground on its side, on which the name of 
the substance may be written in pencil, or with 
waterproof Indian ink. Corrosive and volatile 
substances and solutions, and deliquescent or 
moisture-absorbing chemicals require to be kept 
in bottles provided with well-ground stoppers. 
The stoppers of acid bottles should be rubbed 
round with vaseline, which renders them per- 
fectly air-tight and prevents them from sticking ; 
the same may be done to the stoppers of bottles 
containing caustic alkalis or carbonates, which 
have a slightly corrosive action on glass. Hydro- 
fluoric acid, which attacks glass, must be kept 
in a guttapercha or lead bottle. Dark or orange- 


(Fr., Acide borique; Get., 


Bouteilles, Flacons ; 


B and C. Wide-mouth 
Bottles 


A. Narrow- 
mouth Bottle 


coloured bottles are used for substances that are 
deteriorated by light. Corked bottles are not 
recommended for photographic purposes, except 
for chemicals that will keep well and are not in 
frequent use. They may be rendered air-tight 
by melting wax over the cork and round the 


73 


Box, Negative 


neck, A convenient way of doing this is to hold 
a lighted candle above the cork, allowing the 
melted wax to run all over and around it. (For 
special bottles of various kinds, as collodion 


bottles, dropping bottles, etc, see under 
separate headings.) 
BOX, LANTERN-SLIDE (Fr., Botte aux 


épreuves pour projections ; Ger., Latern- 
bilderkasten, Diapositivkasten) 

A long wooden or metal box with a hinged 
lid, grooved for the storage of lantern slides. 
The ordinary pattern resembles a grooved 
negative box, but some workers prefer plain 
boxes without grooves, and for storage purposes 
only these are sometimes of greater convenience, 
since a number of slides can more readily be 


Lantern-slide Box 


inserted or removed at once; however, tor 
reference or indexing requirements the grooved 
type is preferable. Travelling lantern - slide 
boxes are designed with a view to the prevention 
of breakage; the example shown is fitted with 
a tubber buffer at top and bottom to stop any 
movement of the slides, and has strong brass 
end fasteners and leather straps. The lid is 
furnished with pegs fitting closely into holes in 
the top edges of the box. 


BOX, NEGATIVE (Fr., Boite aux clichés ; 
Ger., Negativenkasten) 

A box, usually either of wood or metal, for the 
storage of negatives. The ordinary grooved 
wooden type is shown at A, but there are several 
other patterns. In one B there is a grooved 
drawer sliding in an outer case, and this offers 
the advantage that any given negative can be 
examined without disturbing other boxes above, 


= 


“i ars SATS AS — SS 
oS SS r 1] pS 
fit f —S 
a 


A. Grooved Box for Negatives 


and possibly without even needing to remove 
the drawer. Either single drawers, which can 
be added to as desired, or drawer cabinets may 
be obtained. Another type of negative box 
has an outer shell made like a book with a label 
to indicate the contents, and having an inner 
grooved case that slips into it from the back, 


Box, Plate 


Grooved metal boxes are also made, with slip-on 
lids. One pattern is an adaptation of the 
card index and vertical filing system, the nega- 
tives being kept in numbered envelopes, on which 


B. Negative Box with Grooved Drawer 


full particulars can be written, and an index 
card is also provided. Guide cards may be used 
to divide or subdivide the negatives, and as 
there are no grooves a good deal of space is saved. 


BOX, PLATE (Fr., Botte aux plaques ; Ger., 
Platienkasten) 

A lght-tight wooden or metal box, usually 
grooved, for the safe custody of unexposed or 
undeveloped plates. Such boxes are made in 
various patterns. Some resemble grooved nega- 
tive boxes, but are more carefully constructed, 
with a deeper lid and rebate. Others A have an 
outer sliding lid, together with an inner lid 
furnished with a spring, which keeps it pressed 


r\ cc. 
satel ! 


1) 


B. Metal Plate Box with Slip-on Lid 


tightly dow21 over the plates when the outer 
lid is in position. Metal boxes with slip-on lids 
and spring dips fastening over the latter B are 
also obtainable. 


BOX-FORM CAMERA (Fr., Détective ; Ger., 
Kastea- Kamera) 

A non-folding hand camera in the shape of 
a box. It ‘s generally of fixed focus, though 
sometimes there is a focusing adjustment. The 
majority of box-form hand cameras have a 
magazine to hold a number of plates in sheaths ; 
or provision is made for carrying roll films, or 
a pack of flat films. (See “‘ Hand Camera.’’) 


71 


Breath Printing 


BOUDOIR 


A commercial size and style of mount largely 
used by professional photographers. The aver- 
age size of a boudoir print is 8 in. by 5 in.—that 
is, a trimmed whole plate, and the mount may 
measure anything from 84 in. by 54 in. upwards. 
Boudoir midget mounts measure about 3% in. 
by 2 in. 


B.P. 


The initial letters of the words ‘“ British 
Pharmacopceia,” which is an official catalogue, 
published from time to time by the General 
Medical Council, giving the standards of purity 
of drugs, etc. The Pharmacopceias of different 
countries vary slightly. The initials, when found 
in a formula, mean simply that the chemical 
named should be of the standard strength and 
purity. 


BRASS, BLACKENING 

Recipes for dead blacks for application to 
brass are given under the heading ‘“‘ Blackening 
Apparatus.” 


BRASS ETCHING 


Brass is etched in intaglio or relief by means 
of ferric chloride, the same as in copper etch- 
ing. The resist image is generally applied by 
the enamel process. 


BRASSES, PHOTOGRAPHING 

Memorial brasses are frequently difficult to 
photograph owing to their position, but unfixed 
brasses may be arranged so that a suitable light 
(preferably a side light) falls upon them. When 
the light or reflections are troublesome, it is a 
good plan to dab the brass with a rag dipped 
in whitening. If the camera is pointed upwards 
or downwards to the brass, take care to have 
the focusing screen—and, of course, the plate— 
vertical, The stop should be small and the plate 
should be a slow or medium one of the isochro- 
matic variety. As a rule, rubbings from old 
brasses make better photographs than the brasses 
themselves. 


BREATH PRINTING (Fr., Impression @ 
Vhaleine ; Ger., Atemkoptieren) 

A curious process, due to Sir John Herschel, 
by which invisible, or latent, photographs may 
be produced, capable of development by the 
breath or by a moist atmosphere. A solution 
of silver nitrate (sp. g. 1-200) is added to ferro- 
tartaric acid (sp. g. 1°023), a precipitate falling 
which is nearly redissolved by a gentle heat. 
A yellow liquid is thus obtained in which the 
further addition of silver nitrate causes no 
turbidity. The total bulk of the silver nitrate 
solution used should amount to half that of the 
ferro-tartaric acid. Paper sensitised with this 
liquid, thoroughly dried in the dark, and exposed 
under a negative or engraving in sunshine for 
from thirty seconds toone minute, does not yield 
any visible impression unless over-exposed. To 
develop the latent image it is only requisite 
to breathe upon the paper, when a vigorous 
picture appears as if by magic. Or the print 
may be laid in a blotting-book, some of the 
outer leaves of which have been damped by 
holding them over warm water. 


Brenzcatechin 


BRENZCATECHIN 

One of the names of the developer popularly 
known as “ Pyrocatechin ” (which see). Known 
also as ortho-dihydroxybenzene, catechol, and 
oxyphenic acid. 


BREWSTER, SIR DAVID 

Born at Jedburgh, 1781; died at Allerly, 
1868. Knighted, 1832. He made many dis- 
coveries in optics, investigated polarisation of 
light, invented the kaleidoscope, and in 1844 
designed the Brewster stereoscope. In 1836 he 
visited Fox Talbot and became interested in 
the latter’s method of producing paper negatives ; 
he also corresponded with Claudet, Ross, Hill, 
and other fathers of photography. He wrote 
many articles and books (about 400), several of 
which dealt with photography. 


BRILLIANCY 

A term implying that a print is bright and 
clear in quality. It generally accompanies a 
long range of tones with strong shadows and 
bright high lights. 


BRISTOL BOARD 

A fine kind of pasteboard made by pasting 
down successive layers of thin paper and having 
a smooth or glazed surface. Its thickness is 
indicated by the terms 6-sheet, 8-sheet, etc. 


BRITISH GUM (See “ Dextrine.’’) 


BROKEN NEGATIVES 


These must not be confused with cracked 
negatives (which see), as they are not treated in 
the same way. Broken negatives are generally 
understood to be those in which the film is broken 
as well as the glass. If the glass only is broken 
the film can be transferred to another piece of 
glass, but this method is not suitable when the 
film as well as the glass is broken, because of 
the danger of distorting or losing the pieces 
during the process of stripping. In many ways 
a mended broken negative is more satisfactory 
than a film that has been stripped and put on a 
new glass backing, and some photographers 
advocate the breaking of the film purposely when 
the glass is cracked in order that it may be 
treated as a broken negative. To mend a nega- 
tive which has been broken into two or more 
pieces, take each piece and clean the edges free 
from dust and dirt. The largest portion is then 
laid upon a clean and perfectly level glass plate, 
and Canada balsam diluted with xylol applied 
to the edges very thinly with a small camel-hair 
brush. Xylol (or xylene) is a coal-tar product, 
and if it is not obtainable benzene can be used 
in its place. The remaining pieces of the 
negative are also touched all round the edges 
with the cement, and are then carefully joined 
so. as to fit exactly. The addition of xylol 
enables one to use the balsam without heating, 
and as it has about the same index of refraction 
as glass, the internal surfaces of the glass, if 
correctly placed together, will no longer reflect 
light, and the breaks will hardly be perceptible. 
The surface of the film is afterwards cleaned with 
a piece of cotton-wool dipped in benzene. Nega- 
tives carefully mended in this way show no sign 
of breakage if printed slowly in the shade. 


72 


Bromide Process 
BROMEOSINE (See “ Eosine.’’) 
BROMHYDRIC ACID (See “ Hydrobromic 
Acid.’’) 
BROMIDES 


Salts formed by the action of bromine on a 
metal, with the characteristic formula M,Br. 


BROMIDE EMULSION (See “ Emulsion.’’) 


BROMIDE ENLARGING § (See 
ing.’’) 


BROMIDE PAPER (Fr., Papier au bromure; 
Ger., Bromsilber papier) 

Paper coated with an emulsion of silver 
bromide in gelatine, for contact printing and 
direct enlarging by natural or artificial light. It 
is prepared with a variety of surfaces. Made 
and introduced commercially about 1874, but 
not on a large scale until 1880. Working details 
are given under the heading ‘‘ Bromide Process.” 


BROMIDE PAPER NEGATIVES 
Bromide paper may be used in place of dry 

plates for negative making. The process is 

described under the heading ‘‘ Paper Negatives.” 


BROMIDE PENCILS (Fr., Crayons au bro- 
mure ; Ger., Bromidptinsel) 

Black crayons used in working-up bromide 
enlargments and prints, platinotypes, etc. They 
are obtainable either in cedar pencils or as 
points for adjustable holders, and are sharpened 
by rubbing on a piece of No. o glasspaper. White 
crayons are also procurable. For a blue-black 
enlargement it is important not to employ a 
brown-black pencil, or the work will show too 
much; and it should be remembered that 
ordinary black chalk drawing pencils have 
frequently a tendency to brownness, 


BROMIDE PROCESS 


The essential feature of the bromide process is 
its suitability for obtaining either contact prints 
or direct enlargements by artificial light, and 
the consequent facilities that it givesfor secur- 
ing any desired result with absolute certainty. 
If a print is produced which is not exactly in 
accordance with the result desired, a second 
exposure may be made while all the conditions 
remain absolutely constant, and tke time of 
exposure may be so modified that the second 
print will give exactly the effect desired. In 
adopting the bromide process, the following 
conditions are desirable. A light that can be 
kept as uniform as possible, a means of fixing the 
relative positions of light and printing frame 
so that the distance between them is always the 
same, and the exclusive use of one trand of bro- 
mide paper. The distance between the light 
and frame should be so adjusted that exposures 
will vary from ten seconds for a moderately thin 
negative up to forty or fifty for a strong or 
dense plate. It is impossible to work accurately 
if exposures are as short as two or three seconds ; 
such exposures cannot be timed with certainty, 
whereas longer exposures can be timed with an 
inappreciable percentage of error. Correctness 
of exposure is absolutely essential in bromide 


“ Enlarg- 


Bromide Process 


printing if good results are desired; there is no 
more fruitful source of imperfect prints than 
incorrect exposure, and the consequent attempts 
to compensate by incomplete or forced develop- 
ment. A perfect bromide print is one that has 
been so exposed that full development with a 
normal solution will give the contrast and depth 
required. In order to expose a print in this 
manner, it will be found desirable to make a 
preliminary trial exposure on a small slip of 
paper, selecting a portion of the plate that has 
part of the densest tones. An ordinary piece of 
paper may be cut into six or eight trial slips, and 
several may be exposed on different negatives 
and developed together. The development of 
these trial slips should be full, in order that the 
correctness of the exposure may be judged 
i the final appearance when in the fixing 
ath. 

Another prolific source of loss of quality in 
bromide work is the system of using one portion 
of developer for several prints in succession. 
The prints last developed are inferior in colour 
and general quality, and if toning is afterwards 
performed, the colour is very poor and weak. 
For prints of moderate size, sufficient developer 
should be taken for one print, the solution used 
once and then thrown away. For small prints 
this is also the preferable plan, but as the quan- 
tity of solution necessary is much larger relative 
to the size of the print, it may be permissible 
to use the same solution for two prints in suc- 
cession, or, better, to develop two prints together. 
But this should be the limit. 

Where practicable, as in the case of an incan- 
descent electric light or an inverted incandescent 
gas burner, the frame should be placed hori- 
zontally below the light for making the exposure. 
It will facilitate shielding parts of the negative 
during the exposure, and also the making of the 
exposure by uncovering and recovering the 
frame, using a sheet of card. 

Diamidophenol and amidol are good developers 
for bromide prints, but they cannot be kept in 
solution satisfactorily for more than three days. 
The seriousness of this objection is realised when 
only two or three small prints are required, and 
then no more wanted for perhaps a week. 
Amidol is, however, a favourite with many 
workers, on account of the fine blue-black colour 
of the prints produced with it. Ortol is also a 
good developer for bromide paper, and it keeps 
for a long time in solution. Metol and hydro- 
quinone form a developer that is a favourite 
with many workers, as it keeps well in solution. 
Excellent formule are as follow :— 


Diamidophenol Developer for Bromide Paper 


Diamidophenol (or amidol) 16 grs. 44g. 
Sodium sulphite # FOO AAci, 
Potassium bromide on ee Bet: bs 
Water 5 8 Oz, 1,000 ccs, 


The sodium sulphite must be dissolved in the 


water first. This solution is used without dilu- 
tion. 
Ortol Developer for Bromide Paper 
A. Ortol : . 4 drms, 54 g. 
Potass metabisulphite 2 ,, oy ae 
Potassium bromide Tus i a ae 
Water . o. REREDEZ. 1,000 ccs. 


73 


Bromine Water 


The potassium metabisulphite must be dis- 
solved in the water first. 


B. Sodium carbonate 2 OZ. 218 g. 
Sodium sulphite gee 218 = 
Water SLOG 1,000 ccs. 


To develop, take 40 minims of A, 80 minims of 
B, and add sufficient water to make 1 oz. 


Metol-Hydroquinone for Bromide Paper 


A. Metol . IO grs. 2°3° g: 
Sodium sulphite 170 4 Eee 
Hydroquinone ass | pte 
Potassium bromide 10 ,, 235 
Water 10 0Z 1,000 ccs, 


Dissolve the constituents in the order given 
in the formula. 


B. Sodium carbonate $ oz. 55 g. 
Sodium sulphite + ,, 7 i ee 
Water 36 1,000 ccs, 


” 


Mix equal parts of A and B to form the work- 
ing developer. 

All these formule produce rich prints of a 
good, pure colour, which will tone quite satis- 
factorily. Full development will take about 
three minutes with the diamidophenol and metol- 
hydroquinone formule, and four minutes with 
the ortol, The print should be soaked in 
water for about half a minute, the water then 
drained off, and the developer flowed evenly 
over the surface, the dish being rocked until 
development is completed. Then the print 
should be rinsed and immersed in the fixing 
bath, taking care that the prints do not cling 
together and that the solution has free access 
to their surfaces. An acid fixing bath is prefer- 
able, containing 1 oz. of potassium metabi- 
sulphite to 1 Ib. of “hypo,” the solution being 
so mixed that 1 pint should contain 3 oz. of 
“hypo.” The prints should remain in the fixing 
bath for fifteen minutes, and should afterwards 
be thoroughly washed. From one to two hours, 
in water frequently changed, according to the 
frequency of the changes, and the number of 
prints in the dish, should be sufficient. 

Daylight can also be used for bromide work 
if desired, and many prefer it for enlarging pur- 
poses, though it is not suitable for contact 
printing. (See also “ Enlarging.’’) 


BROMIDE OF URANIUM PLATES 

Plates coated with a silver bromide collodion 
emulsion containing a small quantity of uranium 
nitrate to keep it free from fog; these plates 
are now obsolete. 


BROMINE (Fr., Brome; Ger., Brom) 

Br. Molecular weight, 80. Solubilities, 1 in 28 
water, very soluble in alcohol, ether, and solu- 
tions of alkaline bromides. A deep reddish 
brown liquid giving off at normal temperatures 
an extremely irritating orange vapour. It is 
rarely used in photography except in its salts, 
though bromine water has been suggested for 
bleaching bromide prints prior to sepia toning. 


BROMINE WATER (Fr., Eau bromée ; Ger., 
Bromwasser) 

An orange-yellow solution, formed by shaking 

bromine with water and decanting from the 

excess which settles at the bottom of the bottle. 


Bromised Collodion 


BROMISED COLLODION, OR BROMO. 
IODISED COLLODION (See ‘ Collo- 
dion.’’) 


BROMISER 

A solution of alkaline or metallic bromides 
usually kept in a separate solution and added 
to collodion just before coating the plate there- 
with. (See “‘ Collodion, Wet.’’) 


BROMO-ARGENTOTYPE 
An obsolete name for bromide paper. 


BROMOIL PROCESS 


A process of obtaining pictures by bleaching 
and pigmenting bromide prints; suggested by 
E. J. Wall in 1907. Working details were first 
published by C. Welborne Piper in August of 
the same year, and the modified process, as now 
worked, was introduced in the following month. 

Prints for the ordinary oil-pigment process 
(which see) are made by contact, and as the pig- 
ment process is generally more suitable for prints 
of fairly large size it follows that users of small 
plates must make an enlarged negative before 
they can produce an ordinary oil print. It was 
to obviate this that the bromoil process was 
devised. Essentially, it is a means by which 
a bromide print (which, of course, may be an 
enlargement from a small negative) can be pre- 
pared for pigmenting. Special bromide papers 
for this purpose are obtainable, although many 
of the ordinary brands are equally suitable. 
The print should not be too old, and it should 
possess certain qualities. A flat‘print, or one 
whose development has been curtailed, will 
seldom give a satisfactory result. The exposure 
should be so adjusted that when the developing 
action has been carried to its fullest extent the 
result is a clean, strong print, rather more vigor- 
ous than would be desirable if it were intended 
to remain unaltered. Amidol is a good developer 
for the purpose, a suitable form being 50 gts. of 
dry amidol added to 20 oz. of water in which 
1 oz. of sodium sulphite has been dissolved. The 
print is fixed in plain “‘ hypo ”’ solution, and very 
thoroughly washed. At this stage the prints 
may preferably be dried. Subsequently they are 
re-soaked for a few minutes to facilitate the even 
action of a bleaching solution. A suggested 


formula is :— 
Citric acid : “ibZO BTS: 6 a eo as 
Potassium bromide . 120 ,, eee 
Potassium ferricyanide 120 ,, 225 (5 
Potassium bichromate 240 ,, i ce 
Alum FhaeO re. 50 4, 
Water to 20 OZ. I,000 ccs 

Dissolve in the order given. It is well to 


ctush the crystals, dissolve in hot water, and use 
when cold. ‘This is applied to each print separ- 
ately until the black image is entirely changed 
to a yellowish brown colour. The prints are 
then washed until the bichromate stain is 
removed, and they are then placed for about 
five minutes in a bath containing 1 oz. pure 
sulphuric acid to 20 oz. of water. This is pre- 
pared by adding the acid slowly to the water, 
and as considerable heat is generated it should 
be made some time before use, or blistering of 
the print will result. 


74 


Brush Development 


After a short washing, the prints require five 
minutes’ immersion in a solution of 2 oz. of 
“hypo” crystals and }$ oz. of sodium sulphite 
in 20 oz. of water. <A further washing to elimin- 
ate most of the “ hypo ”’ brings the prints to the 
stage where pigmenting may be proceeded with. 

There are many variations of the routine of 
preparing the print. For example, many workers 
prefer to dry the prints again, and re-soak them 
for pigmenting, Others omit the acid bath from 
the preliminary stage, and use it immediately 
before this second soaking instead. When the 
prints are only soaked in water before pigment- 
ing it is generally advisable to see that the 
temperature of the water is at least 65° F. (about 
18° C.) in order to secure the necessary swelling 
and relief in the gelatine. (For an outline of the 
method of finishing the prepared print by pig- 
menting, see the heading “ Pigmenting.’’) 

A modification of the bromoil process has been 
made for the preparation of lithographic transfers, 
especially in large sizes for poster work. The 
bromide paper used should be the so-called 
“carbon ”’ or velvet surface, and should be of 
a good substance. An enlargement of a half- 
tone negative is made on to the paper, which 
is then developed with amidol, though some 
workers prefer pyro-ammonia. The print is 
fixed and washed as usual. It is next bleached 
in the usual bromoil bleaching solution at a 
temperature of 75° F. (about 24° C.) for two 
minutes; soaked in a 5 per cent. solution of 
sulphuric acid for six minutes ; washed in several 
changes of water for five minutes; fixed in 
“hypo ” or toned with sodium sulphide for one 
minute; washed in water for five minutes ; and 
dried thoroughly. It is inked all over with a 
composition roller charged with lithographic 
printing ink thinned with turpentine, until a 
thin even coating is laid upon the surface; five 
minutes or so is allowed for the turpentine to 
evaporate completely, and the print is then 
immersed in water at about 70° F. (about 21° C.), 
and after soaking for about half an hour the 
transfer may be developed in exactly the same 
way as an ordinary bichromated gelatine transfer. 


BROMO-IODIDE OF SILVER (See “Silver 
Bromide.’’) 


BRONZED PRINTS 


Prints on certain makes of papers which have 
a metallic appearance when held at a suitable 
angle. The effect occurs chiefly upon self-toning 
papers and sometimes upon platinum prints, 
more particularly when the print has been 
over-exposed or made from a negative having 
very clear shadows. The more sensitive the 
paper the more likely are the deep shadows to 
be bronzed. Bronzed shadows may be elimin- 
ated usually by applying a print varnish, or 
rubbing with wax or encaustic paste, 


BROWN TONES (See “Sulphide Toning,” 


etc.) 


BRUSH DEVELOPMENT 

The development of negatives, bromide prints 
and platinum prints by applying a suitable 
developer by means of a brush instead of immers- 
ing in the developer. For negatives the slower- 


Brush Development 


working developers, such as pyro, are more suit- 
able than the rapid kinds, such as rodinal, metol, 
etc. It is usual to soak the plate in a very weak 
developer until the image just begins to show, 
and then to rinse in water and apply the weak 
developer, or even a normal developer, by means 
of a camel-hair mop, giving the partially devel- 
oped negative repeated rinses in water in order 
that there may be no distinct line of demarca- 
tion. Where a sharp line is wanted, glycerine 
may be mixed with the developer. The brush 
method enables parts of the negative to be 
subdued or accentuated in a wonderful manner. 
The process is perhaps of the greatest service 
in portrait work where white dresses are likely 
to give undesired effects. It is more widely 
used in the United States than in England, and 
_R. W. Phillips, an American, recommends the 
following method of brush development for por- 
trait work; a three-solution pyro-soda formula 
is used: A. Water 20 oz., sodium sulphite 
4 0z.; when dissolved add enough pure acetic 
acid to turn blue litmus paper red, then add 1 oz. 
of pyro. B. Water 16 oz., sodium sulphite 
40z. C, Water 16 oz., sodium carbonate 4 oz. 
To make a normal developer add 1 oz. of each 
of the three solutions to 8 oz. of water. For 
brush development two working solutions are 
made up, one the normal developer given above, 
the other being the same, except that the car- 
bonate is omitted. Then use a separate solution 
of one-half carbonate and one-half water, or 
two-thirds carbonate and one-third water, which- 
ever is found to suit the strength of the negative 
desired. In the case of a plate exposed on a 
sitter in white drapery, develop until the image 
shows faintly, then pour off this regular developer 
and wash the plate. Next pour on the pyro and 
sulphite solution previously made up, hold the 
negative horizontally up to the light in the hand, 
and with a camel-hair mop saturated with the 
carbonate solution rub over that portion of the 
negative which is to appear the most pro- 
minently. This must be done the first time very 
quickly, putting the negative back into the 
solution immediately. The operation is then 
repeated, the carbonate being well blended over 
the plate so as not to show streaks and defined 
lines. 

The principle involved is this: the negative 
is developed only to a slight extent in the first 
immersion, and as soon as the pyro and sulphite 
solution is poured on development practically 
ceases. Then the high lights are controlled 
absolutely with the carbonate solution. Some 
little practice is necessary in order to get a per- 
fect result. Over-exposed negatives are unsuit- 
able for brush development, the control being 
so difficult. 

It is found rather difficult to carry out delicate 
work of this character in the dark-room, and 
there is a very serious risk of exposing the plate 
too freely to the light, and so producing fog and 
loss of quality. 

In bromide printing, brush development is 
very frequently adopted for large prints. A 
smaller quantity of developing solution can be 
employed than most workers could use satis- 
factorily in a dish, though the results produced 
by the brush method are almost always inferior 
in richness and quality to those obtained in the 


75 


Brushes 


ordinary manner. The print is thoroughly 
wetted, so that it will lie perfectly flat on a 
Sheet of glass, and the developing solution 
brushed rapidly over its entire surface in the 
manner described under the heading “ Brush 
Toning ” 

Platinotype prints may be developed with 
a brush if glycerine is mixed with the developer, 
(See ‘‘ Platinotype Process.") 


BRUSH TONING 

A method of toning in which the solution is 
applied by means of a brush. This method is 
occasionally adopted for large prints. A con- 
centrated solution is employed and the print, 
after washing, is laid on a sheet of glass and the 
solution rapidly brushed over its entire surface. 
It is desirable to cover the print with the toning 
solution as quickly as possible, and each stroke 
of the brush must slightly overlap the part 
wetted by the preceding stroke; also, no part 
of the print must be left uncovered in the first 
application, or uneven toning will result. The 
brush strokes are first made along the print, then 
across, and then diagonally, continuing the work 
until the toning is completed. 

Prints, particularly those on bromide paper, 
can be brush-toned to two or more colours, 
The method is widely used for the rapid toning 
of ordinary gelatine or collodion P.O.P., and 
almost every formula can be adapted, but the 
following is considered to be the most suitable. 
Four stock solutions are necessary :— 


No. 1. Ammonium sulphocyanide 1 oz., water 
to 9 oz. 
No. 2. Sodium phosphate 1 oz., water to 9 oz. 


No. 3. Saturated solution of borax. 
No. 4. Gold chloride solution 1 gr. to 1 drm. 


To make up a working mixture take 14 minims 
of No. 1 and make up to1 drm. with water ; then 
add 12 drops of No. 4 very slowly, shaking the 
mixture after each drop is added. Then add 
6 minims of No. 2, and finally 16 minims of No. 3. 
Each ounce of the working solution referred to 
above contains practically 7 grs. of sulpho- 
cyanide, 1 gr. of gold chloride, 5 grs. of phosphate, 
and 7 gts. of borax, and the bath, if desired, may 
be made up by adding these quantities to each 
ounce of water used. By this method, the print 
exactly as it comes from the printing frame, is 
placed on a sheet of glass or pinned to a board, 
and the. working solution brushed quickly and 
evenly over it with a camel-hair mop. Toning 
should be complete in about two minutes, after 
which it is washed and fixed as usual. 

Great care should be taken not to expose 
the print to a strong light during the process 
of toning as otherwise there will be a risk of 
discolouring the whites. 


BRUSHES (Fr., Brosses; Ger., Pinsel) 

The most suitable brushes for mounting, 
colouring, and other photographic operations will 
be found described under their respective head- 
ings. The two brushes (always home-made) 
most widely used in the dark-room are the 
Blanchard and the Buckle brushes, The Blan- 
chard brush A is made by taking a strip of glass 
about 6 in. long and 2 in. wide, and attaching to 
one end wne or two thicknesses of swan’s-down 


Bubbles in Lenses 


calico, wrapping it round the end and fastening 
by means of an elastic band or thread. The 
Buckle brush B is made by drawing some cotton- 
wool, by means of a loop of silver wire or strong 
thread, partially through a glass tube, so that 
a tuft protrudes. Both these brushes are con- 


B. Buckle Brush 


venient instruments for all kinds of photographic 
uses, as either the cotton-wool or the swan’s- 
down may easily be renewed. The Blanchard 
brush is mostly used for applying sensitising 
solutions. 

The Atzpinsel (which see) is a special brush 
used by process workers. 


BUBBLES IN LENSES 

Small bubbles (or air-bells) are occasionally 
seen in even the best of photographic lenses, 
but generally they are no detriment. Their 
presence, even under the most unfavourable 
conditions, does not occasion a loss of light 
exceeding 15 per cent., and their influence upon 
the optical efficiency of a lens system is there- 
fore of no moment whatsoever. The efforts of 
opticians during recent years to improve lenses 
in their higher optical characteristics have led 
to more extended use of glasses that differ widely 
in their optical properties and chemical com- 
position from the crown and flint glass hitherto 
employed, and still used for commoner lenses. 
Their manufacture is attended by greater 
technical difficulties, and it is no easy matter 
to secure perfect freedom from air bubbles. 


BUBBLES ON PLATES AND PAPERS 
Bubbles or air-bells frequently form on plates 
and papers during development, and they have 
the effect of preventing the developer acting 
on the spots covered by them. The result is 
clear glass spots upon the negative or white 
spots upon developed prints. Bubbles invariably 
arise from stale or frequently used developer, 
particularly pyro, or they are caused by a care- 
less and uneven flowing of the solution over the 
surface to be developed. Soaking the sensitive 
material in water previous to development also 
causes bubbles to form on the film. A huge crop 
of tiny clear spots—the result of bubbles—of an 
irregular form and appearing mostly at or near 
the edges of the negative, is generally due to 
an old or oxidised developer, or to one that has 
been allowed to stand even for a short time after 
mixing. Larger, round spots are caused by 
bubbles which attach themselves firmly to the 
sensitive surface during a preliminary soaking in 


76 


Bullets, Photographing 


water, or when the developer is poured on rashly 
and unevenly. Spots with small black centres 
are also caused by bubbles; these form during 
development and cause the gelatine under them 
to be harder than the developed portions, and 
therefore slower in fixing, the result being the 
small specks of unfixed silver bromide in the 
centres of the spots. The methods of preventing 
bubbles are obvious. The plate or paper should 
not be soaked in water before the developer is 
applied ; the developer should be freshly mixed, 
and poured on to the sensitive surface in an even 
sweep, first along one edge, and the dish then 
tilted so as to cover the surface as quickly as 
possible; the dish should be rocked slowly and 
regularly, and not violently and in sudden jerks. 
Many workers pass a clean broad camel-hair 
brush, a pad of cotton-wool, or a Buckle brush 
over the film as soon as the developer is poured 
on, so as to break up and remove any possible 
bubbles; the brush must, however, be quite 
clean and soft, or the remedy will be worse than 
the disease. 


BULLETS IN FLIGHT, PHOTOGRAPHING 

The first attempt to photograph a projectile 
in flight is said to have been made at Woolwich 
Arsenal in 1860. Owing to the slow wet-plate 
process used, the results were unsatisfactory. 
In 1884 some experiments were made at Prague 
by Mach and Wentzel which were far more 
successful; these were on the lines described 
below. In 1887 an improvement on the Prague 
results was made by Drs. Salcher and Riegler, 
of Fiume. 

Probably the most important experiments in 
the photography of flying bullets were those 
published in 1892 by Prof. C. V. Boys, a full 
account of which will be found in the Journal 
of the Royal Photographic Society (April 30, 
1892). His procedure was partly suggested* by 
Lord Rayleigh’s methods of obtaining photo- 
graphs of drops, breaking soap bubbles, etc., 
which were taken by the light of an electric spark. 
The following description of the two chief 
methods employed by Prof. Boys are due to the 
above-mentioned publication. 

The first is shown diagrammatically at A. 
J is a fulminating pane or condenser of small 
capacity, which may be charged on its two sides 
respectively, positively + and negatively —, 
by means of any kind of frictional or induction 
machine. This pane is allowed to discharge 
through a very short circuit in which are two 
gaps Ss'. The spark at s is allowed to shine on 
the photographic plate Pp without the intervention 
of lenses of any kind. ‘The spark at s! is hidden. 
A second condenser, the jar 7 (of very small 
capacity compared with the pane J), is con- 
nected to J, one coating by means of wire, as 
shown by the full lines, and the other by means 
of a string wetted with a solution of calcium 
chloride, as indicated by the dotted line. Its 
coatings, therefore, till the time of discharge 
attives, are kept at the same potentials as 
those of the pane J. The discharge circuit of 
j includes the gaps s!and n. The potential is 
so chosen that neither condenser is able to 
discharge across the two gaps ss! or ns! 
as the case may be, but that either 
would go off if either of its gaps were 


Bullets, Photographing 


made conducting. This is effected by the 
passage of the bullet across , which immediately 
causes a feeble spark at s!, due to the discharge 
there of 7. The air here, being now conducting, 
no longer prevents the pane j from discharging 
across the gap s, and therefore a spark is pro- 
duced which casts upon the photographic plate 
a shadow of the bullet, and in effect an image 
of any atmospheric phenomena accompany- 
ing the bullet. The difficulty in photographing 
bullets is to obtain a spark which, while it 
is bright enough to act on the plate, is yet 
of such short duration that the bullet has 
not time to move more than a hundredth 
of an inch or less while it is yet in existence. 
If glass lenses are used a large proportion 
of the actinic rays are absorbed (in the case 
of a spark between magnesium terminals, four- 
fifths of the whole); but in the case of a 
true image any spark formed by the bullet at 


n 
CEE 


B. Modification of 
of Method A for 
Photographing Bullet 


A. Arrangement for 
Photographing Bullet 
in Flight 


m is properly focused by the camera lens, and 
does not much interfere with the result. If 
lenses are not used the whole of the rays (except 
such as may be absorbed by the air) are effective, 
but any spark at n, being near the plate, would 
fog it so completely as to make the more dis- 
tant spark at s almost, if not quite, inoperative. 
This difficulty is completely avoided by the use 
of the jar 7, of very small capacity, which is 
unable to produce a spark of any appreciable 
photographic effect. Moreover, the spark at 
s is brighter, and should last less time when a 
very short discharge circuit is employed than 
the corresponding spark produced in the dis- 
charge through a greater length of wire, such, 
for instance, as would be necessary if the 
main discharge were taken to the bullet and 
back, 

The second method is a modification of the 
first, and was arranged to meet those cases 


af 


Burgundy Pitch 


where difficulty might arise in closing the gap n. 
In the first arrangement the gap m must be more 
perfectly closed than is the small space s, in 
order to make the action of what may be called 
the “spark relay’ certain. By the introduction 
of a second pane or jar (see B) J? in series with J}, 
the potential of the little jar 7 may be made 
m-+TI times that of j! if the capacity of j? is 


that of jl. 


affected, so it will be necessary to discharge j? 
also before beginning a new experiment. 

The above sufficiently indicates the principle 
of the electrical arrangements. With regard to 
the practical details, the apparatus mostly used 
consisted of a box lined with black cloth, in 
which the photographic plate was placed. The 
large condenser was a plate of glass about a foot 
Square, and the small condenser was a jar or 
bottle to act as a starter for the spark. The 
bullet enters and leaves the box by two holes 
covered with paper to exclude the light, and 
in passing in front of the plate it touches the 
terminals of two thin lead wires, thus completing 
the circuit and causing two flashes—a small one 
which does not affect the photographic plate, and 
a larger one which does affect the plate, and has 
a duration of less than one-millionth of a second. 


BULL’S-EYE CONDENSER 

A plano-convex (almost hemispherical) lens, 
mounted upon a stand and fitted with a universal 
joint. Itis used in microscopy to focus the light 
upon the object, or upon the substage mirror, 


In the discharge, only j! is 


Bull’s-eye Condenser 


and is almost indispensable when examining or 
photographing opaque objects. Also it is useful 
for improving the illumination of transparent 
specimens. 


BURETTE 

An apparatus used in volumetric analysis to 
deliver accurately measured quantities of liquids. 
It consists of a glass tube of uniform bore, 
graduated, and usually fitted with a stop-cock 
at the bottom from which any desired quantity 
of a liquid can be allowed to flow from the tube. 
A modified form working after the manner of a 
fountain-pen filler is used for measuring small 
quantities of photographic solutions. 


BURGUNDY PITCH (Fr., Poix blanche 
Bourgogne; Ger., Burgunderpech) 


The resin of Abtes or Pinus excelsa, the spruce 
fir, purified by melting in hot water and 


de 


Burnett’s Process 


straining. True Burgundy pitch is not easy to 
obtain, and a fictitious article is often sold for 
it. The true resin is translucent and has a dull 
yellowish brown colour, and the fracture is 
shining and conchoidal; some examples contain 
much water, and are opaque and of a dull grey 
colour; they require straining to free them 
from impurities. The odour is peculiarly aro- 
matic and characteristic, It is not wholly 
soluble in alcohol of -838, a little flocculent white 
matter being left; much the same happens if 
placed in contact in a vial with twice its weight 
of glacial acetic acid. It is very soluble in 
acetone. The false Burgundy pitch is usually 
brighter in colour than the true, with a weak, 
scarcely aromatic odour; it is less soluble in 
alcohol, and in glacial acetic acid it forms a 
turbid mixture separating into two layers, a 
thick, oily liquid above and a bright solution 
below. Burgundy pitch is used in process work 
in the preparation of photo transfer inks, In 
solution with spirit of wine it forms an excellent 
aquatint etching ground. 


BURNETT’S PRINTING PROCESS 


One of the many printing processes employing 
uranium ; invented by Burnett in 1857. 


BURNISHER (Fr., Presse a satiner a chaud ; 
Ger., Hetsssatiniymaschine) 

A machine for imparting a glossy surface to 
prints by pressure and friction against a heated 
and polished bar or roller. The bar burnisher A 
—the older type—has a polished steel or nickelled 


78 


Burton, W. K. 


must be avoided. The prints should not be 
quite bone dry, and if kept too long they do 
not burnish so well. On the other hand, they 
must not be damp, or they may blister and stick 
to the bar or roller. 

When a bar burnisher is used, the prints will 
require, before burnishing, to be lubricated by 
rubbing with a mixture consisting of 4 grs. of 
castile soap dissolved in 1 oz. of alcohol, applied 
with a tuft of cotton-wool. To dissolve the soap, 
the bottle containing the mixture is placed in hot 
water, The print is passed through the burnisher 
face downward, pulling it upward in a slightly 
cutved direction from the back as it goes through. 
This is done three or four times. When the print 
is passed through flat, without pulling it, whether 
in a burnisher or a rolling press, hot or cold, the 
operation is known as “‘ rolling’; but this term 
is frequently applied indiscriminately to burnish- 
ing also. 

With a roiler burnisher, a lubricant is not 
required, Solid rollers take some time to get 
hot and require to be rubbed lengthwise with a 
soft cloth until heated, meanwhile revolving the 
roller backwards ; this is to prevent the deposi- 
tion of condensed moisture from the air, due to 
the lower part of the machine getting warm first, 
while the roller is still cold; this moisture, 
if allowed to settle and dry on, would make 
the roller dull and streaky, and might cause 
rust. 

The more modern burnishers have a hollow 
roller with the gas burners inside it; this gets 
hot in a much shorter time, and the heat is also 


A. Bar Burnishet 


bar and merely a single roller; while the roller 
burnisher—or, as it is sometimes called, ‘‘ enam- 
eller’? B—has two rollers, one or both being of 
polished nickel. The bar burnisher is said to 
give the better gloss, but has the disadvantage 
that the prints need lubricating, and they occa- 
sionally get scratched. Both kinds are heated by 
spirit or gas, or with hollow rollers steam is 
sometimes employed. Rolling presses, properly 
so-called, have a large flat steel plate and a 
single polished roller, and are used either with 
or without heat. 

Burnishers of agate or other stone have had 
in the past a few photographic uses. (See “ Agate 
Burnisher,’’) 


BURNISHING (Fr., Satinage; Ger., Satini- 
ven) 

The method of obtaining a glossy surface on 
P.O.P. and albumenised prints by drawing them 
through a heated burnisher. For P.O.P the 
bar or roller of the burnisher should be just too 
hot to be touched with the finger, and for albu- 
menised prints a trifle hotter, but excessive heat 


B. Enameller or Roller Burnisher 


more even. A screw adjustment is usually pro- 
vided for regulating the distance between the 
rollers, bar burnishers having instead nuts under 
the plate, or some similar arrangement. Should 
the steel bar of a bar burnisher become scratched 
it should be rubbed carefully with a slip of fine 
oilstone having a little sweet oil on it, until 
uniformly smooth and bright. The oilstone 
should be held flat on the bar and drawn 
from end to end only, not across. Nickelled 
rollers are difficult to repolish satisfactorily 
when worn, and generally require sending to be 
teplated. 


BURNT-IN PHOTOGRAPHS (See 
amic Photography.’’) 


BURTON, W. K. 

Born in Scotland, 1853; died at Tokio, Japan, 
1899. Author and experimentalist ; first became 
prominent in the early ’eighties as an authority 
on the theory and practice of emulsion making, 
Burton was an engineer by profession, and early 
in 1887 left for Tokio, where, at the Imperial 


** Cer- 


Buttonhole Camera 


College, he was appointed to a professorship. He 
compiled an exposure table and published an 
““A BC of Photography.” 


BUTTONHOLE, OR VEST, CAMERA (Fr., 
Chambre a boutonniére ; Ger., Knopfloch- 
Kamera) 

A small detective camera of circular form, 
somewhat like a large watch, and worn under 


Button-hole Camera 


the vest, as shown in the illustration. The lens 
protruded through a buttonhole. Six round 
pictures about the size of a penny were taken 
in succession on a circular plate. The device 
was invented by Stirn. 


79 


Buttons, Photographic 


BUTTONS, PHOTOGRAPHIC 

Celluloid buttons containing photographs. 
Ordinary prints are first prepared, these being 
albumen, P.O.P., or bromide, and after fixing, 
washing, and drying, they are mounted face 
down with starch or gelatine on sheets of cellu- 
loid sold for the purpose. If necessary, the 
photographs may be mounted before they are 
dried. When dry the photographs are cut out 
with a punch or die, placed in a machine with 
the metal discs, and stamped into buttons. The 
bent pin, strut, or frame is then attached. 


Gas-heated Roller and Metal Plate 


Professional workers use a gas-heated roller 
and metal plate, as shown. The dry print is 
immersed in alcohol till both sides are moistened. 
A sheet of blotting-paper is placed on the plate, 
then the celluloid, next the print, face down, and 
finally a piece of tissue paper. The roller, 
sufficiently hot to sizzle when touched with 
water, is now passed over all, uniting the print 
and celluloid, 


C 


0 DE. Wi"2 
The abbreviated form of 
(which see). 


‘**CABINET’’ SIZE 

A popular size of professional portrait, having 
a mount measuring 6% in. by 44, in. The actual 
print may be 54 in. by 4 in., 5? in. by 4 in., or 
6 in. by 4} in., these being known in the 
trade ‘as! No, 1,” .*Nos 72,0 and Special © 
cabinet sizes respectively. Cabinets were in- 
troduced in 1867 by F. R. Window, of 
Baker Street, London, who, as a professional 
photographer, found the then popular carte- 
de-visite too small for groups and for ladies’ 
dresses, possibly crinolines, which were fashion- 
able between 1856 and 1867, 


CACHET, ROUGE ET VERT 

Names once given to some French isochrom- 
atic plates, ‘‘rouge”’ being of medium rapidity 
and ‘‘vert’”’ special rapid. A French chemist 
(Tailfer) was the first to make a _ successful 
isochromatic dry plate (1882). The British rights 
to the patent were secured in 1886 by B. J. 
Edwards & Co. 


CADMIUM BROMIDE (Fr., Bromure de cad- 
mium ; Ger., Bromcadmium) 

CdBr,, or CdBr, 4H,O. Molecular weights, 
272 and 344. Solubilities, 1 in 0-94 water, 1 in 
3 alcohol, 1 in 250 ether, 1 in 16 alcohol and ether. 
A yellowish crystalline powder, obtained by 
heating cadmium to redness in bromine vapour. 
It is used to bromise collodion. 


CADMIUM ‘CHLORIDE (Fr., Chlorure de cad- 
mium ; Ger., Chlorcadmium) 

CdCl, or CdCl, 2H,O. Molecular weights, 183 
and 201. Solubilities, 1 in 0-71 water, 1 in 8 
alcohol. It occurs as small white crystals, which 
are occasionally used in collodion emulsions. 


CADMIUM IODIDE (Fr., Jodure de cad- 
mium ; Ger., Iodcadmium) . 

CdI,. Molecular weight, 366. Solubilities, 1 in 
1:08 water, 1 in 1 alcohol, 1 in 3-6 ether. It 
takes the form of colourless flaky crystals. 

This salt is preferred for iodising collodion for 
process negatives, generally in conjunction with 
ammonium iodide. 


CADMIUM-AMMONIUM BROMIDE (Fr., 
Bromure double de cadmium et d’am- 
monium ; Ger., Zwetfach-ammonium-cad- 
miumbromid) 

2CdBr, 2NH,Br H,O. Molecular weight, 758. 

Solubilities, 1 in 0-73 water, 1 in 5-3 alcohol, 1 in 

24 of equal parts alcohol and ether. A double 

salt suggested by Eder on account of its greater 

stability for collodion processes, It can be pre- 


** carte-de-visite ”’ 


80 


pared by dissolving 344 parts of crystallised 
cadmium bromide and 98 parts of ammonium 
bromide in water and then crystallising. 


CADMIUM-AMMONIUM IODIDE (Fr., Jo- 
dure double de cadmium et d’ammonium s 
Ger., Zwetfach-ammonium-cadmiumiodid) 
CdI, 2NH,I 2H,O. Molecular weight, 692. 
Solubilities, 1 in 0-58 water, 1 in 0-70 alcohol, 
I in 1-8 equal parts alcohol and ether. A double 
salt suggested by Eder, as it gives greater 
sensitiveness to collodion than the single salts. 
It can be prepared by dissolving 145 parts of 
ammonium iodide and 183 parts of cadmium 
iodide in water and then crystallising. 


CALCIUM BROMIDE (Fr., Bromure de cal- 
cium; Ger., Bromcalcium) 

CaBr,. Molecular weight, 200. Solubilities, 
I in 0:7 water, very soluble in alcohol. Very 
deliquescent. Should be kept well stoppered. 
A white, granular powder, obtained by neutralis- 
ing hydrobomic acid with chalk. It is used in 
making collodion emulsion. 


CALCIUM CARBIDE (Fr., Carburve de cal- 
cium; Ger., Calctumkarbid) 

CaC,. Molecular weight, 64. It is decomposed 
by water, and extreme care must therefore be 
exercised in storing free from moisture. It 
occurs in greyish-black, irregular lumps, or 
sometimes in coarse granules, and is obtained 
by direct union of lime and carbon in the electric 
furnace. On being added to water acetylene 
gas (which see) is evolved, slaked lime being left 
as a residue: Ca C,+H,0=C, H,+Ca0. 


CALCIUM CARBONATE, OR CHALK (Fr., 
Carbonate de chaux; Ger., Kreide, 
Kohlensaures Kalk) 

CaCO;. Molecular weight, 100. Solubilities, 
insoluble in water, alcohol, or ether. Prepared, 
or drop, chalk foccurs as a white amorphous 
powder or small cones, and is obtained by wash- 
ing native chalk. Precipitated chalk is obtained 
by precipitation from a soluble calcium salt by 
a carbonate, and should alone be used in photo- 
graphy, as it is freer from impurities; it is an 
impalpable white powder, and is used to neutral- 
ise toning baths. 


CALCIUM CHLORIDE (Fr., Chlorure de cal- 
cium ; Ger., Chlorcalcium) 

CaCl, (anhydrous), CaCl,6H,O (crystal). 
Molecular weights, anhydrous 111, crystal 219. 
Solubilities, 1 in 1-4 water (anhydrous), 1 in 0-25 
water (crystal), soluble in alcohol. It is extremely 
deliquescent, and must therefore be kept well 
stoppered. The pure anhydrous salt occurs as a 
white, granular powder, in sticks or lumps; the 
hydrated salt as white crystals; both are used 
occasionally in emulsion making. 


Calcium Chromate 


The commercial granulated dry chloride 
(CaCl, 2H,O) occurs in greyish-white porous 
masses about the size of a pea, and is used as 
a desiccating agent for platinotype and other 
papers. When from absorption of moisture it 
becomes a pasty mass, it can be easily dried 
in an ordinary oven. 

In process work, calcium chloride is used in 
iodisers for collodion. The dry commercial variety 
of calcium chloride in hard lumps is used for 
placing in drying boxes for carbon tissue, gela- 
tine films, etc. Also it is used in calcium tubes 
for storing sensitised paper. 


CALCIUM CHROMATE (Fr., Chromate de 
calcium; Ger., Calciumchromat) 

CaCrO, 2H,O. Molecular weight, 192. Solu- 
bilities, soluble in water and alcohol. It is a 
yellowish powder, prepared by neutralising 
chromic acid with chalk. It was suggested by 
Valenta as an addition to printing out emulsions 
to obtain greater contrast, and he gives the 
following method of making a Io per cent. 
solution :— 


Chromic acid (pure) 386 gers. 
Distilled water to 34 02. 


Dissolve, and add sufficient precipitated chalk 
to make the solution permanently milky after 
well stirring. Filter, and wash the filter with 
sufficient distilled water to make 82 oz., or 
250 ccs., in all. 


CALCIUM HYDRATE, OR HYDROXIDE 

Ca(OH),. Molecular weight, 74. A synonym 
for slaked lime, a substance which has been sug- 
gested as an addition to the gold toning bath, 
but is very rarely used. 


CALCIUM HYPOCHLORITE (Fr., Chlorure 
de chaux, Chlore & blanchir ; Ger., Chlor- 
kalk) 

Synonyms, bleaching powder, chloride of 
lime. Solubilities, 1 in 400 water, 1 in 7°5 alcohol. 
It is poisonous, the antidotes being ammonia 
vapour, steam, ether vapour, and dilute sul- 
phuretted hydrogen. It occurs as a white or 
greyish-white powder with powerful chlorine 
smell, and is obtained by passing chlorine gas 
over slaked lime. Its composition is doubtful, 
but may be considered to be approximately 
Ca(OCl)Cl. It is used for preparing Labar- 
raque’s solution and Eau de Javelle (which see). 


CALCIUM SULPHATE (Fr., Sulfate de cal- 
cium; Ger., Calciumsulfat) 

Synonyms, sulphate of lime, 
CaSO, 2H,O. Molecular weight, 172. Solu- 
bility, 1 in 380 water. It occurs naturally as 
the mineral anhydrite CaSO,, and, in combina- 
tion with 2H,O, as alabaster, gypsum, satin-spar 
and selenite. Gypsum when heated moderately 
loses its water, becoming what is known as 
plaster-of-paris, which, when mixed to a paste 
with water, again takes up 2H,O and sets toa 
hard solid with expansion. Plaster-of-paris is 
used for making casts and moulds in some 
photo-mechanical processes, and for photographic 
bas-reliefs. It is sometimes useful for stopping 
leaks and repairing broken articles. It should 
be kept in air-tight stoppered jars, and only the 

6 


25 g. 
IOO CCS. 


gypsum, 


81 


Calotype Process 


finest quality should be used for photographic 
purposes. Calcium sulphate is a common 
impurity in spring water, causing what is known 
as permanent hardness, which is not removed 
by boiling. 


CALCIUM TUBE 


A tube or box, usually of “tin ’”’ (tin-plate), 
divided into two parts, the larger for storing 
paper and the smaller for containing calcium 
chloride. The illustration shows a good home- 
made pattern. The larger tin holds the sensitive 
paper, which rests upon a smaller tin having a 
perforated top and containing the chloride. 
Such tins may be used for all kinds of paper 
likely to be affected by damp, and, indeed, are 
necessary for keeping platinotype paper dry 
and in a good printing condition. The calcium 
chloride absorbs the moisture. Platinotype 
paper is sold in air-tight tins, each of which 
contains a twist of paper or cotton-wool hold- 
ing a small piece of asbestos, which has been 
saturated with calcium chloride; this may be 
used over and over again by heating on a red- 
hot shovel to drive out the moisture. Should a 


Calcium Tube 
new piece be required it may be prepared by 
taking a saturated solution of calcium chloride, 
adding to it coarse commercial asbestos, and 
kneading the whole into small cubes, afterwards 
drying them in an oven. Calcium chloride may 
be purchased in the anhydrous form and used 
in place of the asbestos; it should be tied up 
in fine muslin or placed in a small perforated tin, 
care being taken to prevent any particles of it 
getting on to the sensitive paper. 


CALMEL’S POWDER 

A mixture of resin, pitch, and asphaltum 
melted and ground to fine powder for use as 
an acid resist in photo-etching. 


CALOMEL (See ‘‘ Mercurous Chloride.’’) 


CALOSCOPIC LENS (Fr., Objectif caloscop- 
ique ; Ger., Caloskopische Linse) 

A landscape lens made in the late fifties and 
early sixties of the nineteenth century. It was 
designed on the same principles as Petzval’s 
orthoscopic lens. 


CALOTYPE, OR TALBOTYPE, PROCESS 
A negative process upon paper, invented by 
Fox Talbot and patented by him on September 


Camarsac’s Process 


20, 1841. It was the third British patent for 
photography, the two previous ones being for 
the Daguerreotype process. The patent was 
afterwards disputed by the Rev. J. B. Reade, 
but Talbot’s claim was upheld in the law courts, 
mainly for the reason that Reade’s previous dis- 
covery was not properly published or made 
known. Fox Talbot’s process was afterwards 
considerably improved by C. Cundall. The 
original process is briefly as follows: Paper of 
close texture was washed over with a solution of 
100 gts, of silver nitrate in 6 oz. of water. When 
dry, the paper was immersed in a solution of 
potassium iodide, 25 grs. to each ounce of water, 
for two or three minutes, then rinsed in water 
and dried. Paper in this condition was called 
‘“‘iodised paper,’’ and could be stored in a port- 
folio for use as required. Sometimes the double 
operation referred to above was performed at 
one time by brushing a solution of iodide of 
silver and potassium over the paper with a 
Buckle brush. In order to prepare the paper for 
exposure in the camera two solutions were 
necessary: A. 100 grs. of silver nitrate dis- 
solved in 2 oz. of water, to which is added one- 
sixth of its volume of strong acetic acid. B. 
A saturated solution of crystallised gallic acid. 
Equal parts of A and B were mixed together, the 
mixture being called gallo-nitrate of silver. The 
iodised paper was brushed over with this solution, 
ot the paper floated upon it for half a minute, 
then rinsed in water or blotted off, the operations 
being carried out in the dark-room. The paper 
was then placed, either wet or dry, in the dark 
slide and exposed in the camera, the exposure 
necessary being, under good conditions, about six 
minutes. The paper was developed by washing 
over with gallo-nitrate of silver (as above), and 
was fixed, after washing in water, by a minute’s 
immersion in a solution of 100 gts. of potassium 
bromide in 8 oz. of water. Finally it was washed, 
dried, and printed from. 

Modifications of the process consisted in slight 
alterations in the sensitising bath, the use of 
ferric protosuiphate as a developer, and of 
sodium hyposulphite as a fixer, and the making 
of the paper negatives more easily printable by 
waxing or by immersion in almond oil. The 
calotype process was popular between 1841 and 
1851, but was superseded by the collodion process 


CAMARSAC’S PROCESS (Fr., Procédé 
Camarsac ; Ger., Camarsac’s Prozess) 

Lafon de Camarsac was the first, in 1855, 
to discover the method of making burnt-in 
photographic enamels, now known as ceramic 
photographs, or photo-ceramics, and the process 
was in the beginning named after its originator. 
(See ‘‘ Ceramic Photography.’’) 


CAMBOGE (See ‘‘Gamboge.’’) 


CAMEO (Fr., Camée; Ger., Kamee) 

Photographically, a bas-relief portrait finished 
in plaster-of-paris or coloured waxes. (For 
working details, see ‘‘ Bas-reliefs.”’) 


CAMEO PRINTS 


An old type of professional carte-de-visite 
portrait, popular between the ’sixties and 
eighties. It was the invention of Messrs. 


82 


Camera 


Window & Grove, and in its earliest form, called 
‘‘ diamond cameos,” consisted of four positions 
on one card, as A, and raised as medallions. 
Later, one position took the place of four, and 
it became even more popular. After mounting 


A. Cameo Print, 
Medallion Style of Cameo Print backed 
Print with Cotton- 

wool 


B. Convexity C. Cameo 


the print in the ordinary way upon a flat card, 
it was put in a press and made convex, as B. 
Another and a more expensive plan was to make 
only the print convex, and to fill the concave 
part with cotton-wool before pasting it upon 
a flat card, as C. 


CAMERA (Fr., Chambre, Chambre noive ; Ger., 
Kamera) 

The photographic camera is essentially a light- 
tight box, having a lens at one end and provided 
at the other with a suitable arrangement for the 
insertion and withdrawal of the sensitive plate 
or film. To ensure that the required amount 
of subject is included, a ground-giass focusing 
screen, or some kind of finder or sight, is employed. 
The prototype of the photographic camera is 
the camera obscura (which see). The first 
camera used for photography was that of 
Nicéphore Niepce, who, writing in 1816, describes 
it as a box about 6 in, square, furnished with a 
sliding tube carrying a lens. In Daguerre’s first 
camera A the only means of focal adjustment 


A. Daguerre’s First Camera 


was a rack and pinion on the objective. Charles 
Chevalier, of Paris, introduced some improve- 
ments, among them the method of making the 
body in two portions, one sliding within the other 
and clamped by a screw working in a slot on 
the baseboard, as seen in Daguerre’s later appar- 
atus B; this arrangement is still met with in 


Camera 


some ferrotype cameras. The mirror E at the 
back, to erect the image in focusing, will be 
noticed. The next step forward was the inven- 
tion of the bellows, which was probably sug- 
gested by that of the accordion, and seems to 


B. Daguerre’s Sliding-body Camera 


have been known as early as 1839, though it 
was not in general use till the ‘fifties. It 
was ofiginally square or oblong, and the only 
way of reversing the plate was to turn the entire 
apparatus on its side. The pyramidal, or so- 
called ‘conical,’ bellows was first made in 
1861, and at about the same period were intro- 
duced the swing front, swing back, and side- 
shifting movement. Since then progress in 
camera construction has been rapid. The 
reversing back, rising and falling front, turn- 
table, and many other conveniences, have been 
added, until the elaborate and beautifully- 
finished outfits of to-day bear scarcely any 
resemblance to the heavy aud clumsy apparatus 
of earlier years. Yet, to give a curious instance 
of how ideas tend to repeat themselves, the 


Handle 


Reversing 
Back, 


Plumb Indicator 


83 Camera Bag 


an inclined mirror and using it both for focusing 
and as a shutter. D will serve to explain the 
various fittings and movements of a modern 
triple-extension field camera, each part being 
named and indicated by an arrow. The different 


C. Box-form Camera Obscura: Early 
Anticipation of Reflex Principle 


kinds of cameras are described in this work 
under their separate headings as “ Studio 
Camera,” ‘‘ Field Camera,’ “ Hand Camera,” 
“Reflex Camera,’ “‘ Enlarging Camera,’ etc., 
and any not so found should be looked for under 


Bellows Rising Front 


ii Cross Front 
a eam 

i Shutter 
teats. 


Wide-Angle Sa i CD 
Movement eG e, 1AM ays oe 
Ta) on Leet A SN i Front 
é mw, \n 9 PT Extension 
Swing Back fi y tay ‘ \ rf Frame 
| yf / YON" Swing Front 
Back Focusing 
Back Pinion 
Extension Front Focusing Turntable 
Frame Pinion Let into Baseboard 


D. Fittings and Movements of Modern Triple-extension Field Camera 


latest refinement of mechanical skill, the reflex 
or reflector camera, is strikingly similar in design 
to an early pattern of box-form camera obscura 
€ described by the Abbé Nollet in his ‘“‘ Legons 
de Physique,” published at Paris in 1755. 
Thomas Sutton, in 1861, was the first to adopt 
the reflector principle in exposure by hingeing 


the particular branch of work for which it is 
used, 


CAMERA BAG, OR CASE (Fr., Sac 
chambre ; Ger., Schnappsack, Sack) 

A receptacle for the carriage and protection 

of the camera, lens, and slides, commonly of 


a 


Camera Carrier 


canvas or leather, and generally provided with 
a strap to sling over the shoulders. The better- 
class bags are lined with baize, felt, or velvet, 
and have suitable partitions. A lock and key 
is a useful precaution against the dark-slides 
being tampered with when travelling. 


CAMERA CARRIER (Fr., 
Ger., Kameratrager) 

An attachment for carrying the camera, etc., 
on a bicycle or tricycle. Various patterns are 
made, with screw clamps to fit on the front, 
back stays, or handle-bar of the cycle, and 
furnished with straps or spring clips to secure 
the apparatus, There is a general opinion, how- 
ever, that the camera is best carried when slung 
on the rider’s back. (See also ‘‘ Cycle.’’) 


Porte-chambre ; 


CAMERA LEVEL (Fr., Niveau ; Ger., Nivelie) 

A device to enable the back of the camera to 
be kept truly vertical or the base horizontal, as 
For the first purpose, a plumb 


the case may be. 


A. Circular Spirit B. Long Spirit Level 


Level 


C. Quadrant or Two-way Level 


indicator hung at the side is ordinarily employed, 
though a circular spirit level A let into the top is 
sometimes preferred. For the baseboard, either 
a long spirit level B or a circular one is used. 
There are many patterns of levels, some working 
with spirit, others having a small ball enclosed. 
A quadrant or “ two-way” level is illustrated 
at C, 


CAMERA LUCIDA (Fr., 
Ger., Die Helle Kammer) 
An instrument used for delineating views from 
nature and copying drawings. It was a camera 
lucida that Fox Talbot was using when, in 
October, 1833, he began to think out a plan for 
fixing the images seen by its aid, but he at a 
later date put it aside in favour of the camera 
obscura. ‘The camera lucida proper was invented 
by Dr. Wollaston, who died in 1828, but the name 
was originally given to an instrument, invented 

by Dr. Hooke, analogous to the microscope. 
The best form of the camera lucida consists 
of a four-sided prism having the vertical cross 
section ABCD as shown in the diagram. The 
side a B is at an angle of 22} deg. with the hori- 
zontal, while the side B Cc makes the same angle 
with the vertical. A horizontal ray of light from 


Chambre clatre ; 


84 


Camera Obscura 


an object E is twice totally reflected at F and G, 
and emerges vertically from H to J. The eye 
at J refers the ray to a point vertically beneath 
at kK, and at the same time is able to look over 
the edge c of the prism at a sheet of white paper 


J: 
D Hig 
; 
9 
® 
Bi 
hens maaan tests oy : 
0 
‘ 
4 
Ki 
ee ES ee 


Optical Principle of Camera Lucida 


placed below, on which the image of the object 
is seen, and on which it may be traced with a 
pencil. The prism is mounted in a brass case, 
and is fixed by a movable joint to an upright rod 
about 1 ft. high, provided with a clamp at its 
outer end to attach it to a drawing board. 


CAMERA OBSCURA (Fr., Chambre obscure ; 
Ger., Die Dunkelkammer) 

Literally, ‘(dark chamber”; an _ optical 
instrument invented by Baptista Porta in 1569, 
although there is evidence of an even earlier 
knowledge of its principle and properties. This 
simple instrument depends in principle on the 
fact that if a tiny hole is made in the shutter of 
a room from which light is otherwise excluded, 
a small reversed image of the view outside will, 
under favourable circumstances, be thrown on 
the opposite wall. This experiment appears to 
have been known to philosophers from time 
immemorial, but only comparatively recently was 
discovered the improvement effected by using a 
convex lens in place of the hole. Baptista Porta’s 
box-form of camera obscura appears to have been 
used as an entertaining toy, or as a ready means 
of tracing landscapes and views, for nearly three 
centuries prior to the discovery of photography. 
A quaint form of camera obscura, designed by 
A. M. Guyot, for outdoor work in tracing land- 
scapes, is shown in section at A. It resembles 
an ordinary table, the camera being situated 
between the legs and the top being formed by 
a sheet of plain glass M, on which is laid a piece 
of tracing paper. The image formed by the 
convex lens K is thrown upwards on the screen 
mM by being reflected from an inclined mirror I. 
A modification of this device is shown at B, the 
projected image being viewed under cover of a 
dark chamber, at the top of which the optical 
system is arranged. A double convex lens is 
placed in a sliding mount at K, and over itisa 
mirror 1, set at an angle of 45° relative to the 
horizon, As the lens is uncorrected for spherical 
abetration, the image would suffer in definition 
at the margin if received upon a perfectly plane 
surface. Therefore the surface M is made con- 
cave, and part of a sphere whose radius is the 
focal distance of the convex lens K. 

The best form of camera obscura is that in 
which internal instead of specular reflection is 
employed, to prevent the loss of light attendant 


Camera Obscura 


on the latter. The optical system then con- 


sists of a rectangular prism C, having one of its 
faces convex and another concave, such a com- 
bination doing away with the necessity of a 
mitror to change the direction of the rays from 


a 


A. Guyot’s Camera Obscura 


a horizontal to a vertical course. The rays from 
a distant object or landscape will be made to 
converge after impinging on the convex surface, 
and being reflected in the interior of the prism, 
will pass into the dark chamber to the surface 
upon which the picture is to be received. The 
picture thus obtained will be extremely vivid. 
With an optical system of this character, the 
sutface on which the picture is formed may be 
plane and not concave. As these meniscus 
ptisms are difficult to procure, they may be 
replaced by a triangular prism N (see illus- 
tration D), having a plano-convex lens 0 and a 
plano-concave lens Pp, both of proper focal length, 
cemented by Canada balsam on two of its faces. 
Spherical aberration is sometimes guarded 
against by using a plano-concave lens E in place 


fi > Y 


B. Camera Obscura, with Concave Surface to 
receive Image 


of the more complex combination, in which case 
the lens is placed at the top of the dark chamber 
with its concave surface uppermost. With this 
latter arrangement a plane surface suffices to 
receive the picture, but the mirror 1, in illus- 
tration B will still be needed to turn the rays 
from the horizontal to the vertical direction. 


85 


Camera Obscura 


The box-form camera obscura is shown at F, 
and it will be seen that the principle here 
employed is practically the same as that of 
Guyot’s table-form apparatus, with the addition 
of a shade g. This device is sometimes used by 


Prisms and Lenses of Camera Obscura 
employing Internal Reflection 


artists in sketching or, rather, tracing outline 
pictures of landscapes. K is the lens, 1 the 
mirror, and m the sheet of tracing paper, or 
ground glass with the matt surface uppermost. 
The modern photographic camera obscura— 
which will be readily recognised as the reflex or 
reflector camera—is arranged in the same way 
as F, but the lens used at kK is of the compound 
type, in which spherical aberration, achromatism, 
and all the other defects of a simple lens are 
corrected ; so that when the mirror I, is mechanic- 
ally moved out of the path of the rays a perfect 
negative image is received upon the sensitive 
plate, suitably placed at the back of the camera. 

A sterescopic camera obscura devised by 
Theodore Brown is a half-plate instrument fitted 
with a mirror for reflecting the rays on to 
a horizontal screen where the stereoscopic images 
are seen. Unlike an ordinary stereoscopic 
camera, in which a pair of lenses side by side are 
used, only one lens is used, but it is supplemented 
with a double reflecting device (the ‘‘ Stereo- 
photoduplicon,” which see), to be used on the 
hood of the single lens. The effect is very 


F, Diagram of Box-form Camera Obscura 


charming, especially when the face of the 
observer is properly enclosed within the hood or 
shade placed above the screen on which the dis- 
similar images are projected. By turning the 
camera on its axis during inspection of the images 
a panoramic, as well as a stereoscopic, natural 
colour effect is produced. 


Camera Screw 


CAMERA SCREW (Fr., Vis du pied; Ger., 
Stativschraube) 

The sctew attaching the baseboard of the 
camera to the head, or top, of the tripod, in those 
cases when a turntable is not fitted. The loose 
screw is very liable to get lost, and is difficult to 
insert without several ineffectual attempts, in 
which the bottom of the camera frequently gets 
scratched. Several special forms of tripod screws 
have been introduced to avoid these objections, 
among which may be mentioned Renbold’s, 
which is permanently attached to the camera 
and folds into a recess in the bottom when not 
in use. It is tightened on the tripod head by 
means of a nut. 

The Royal Photographic Society recommend 
that all screws fitted to cameras either for 
attachment to the stand, for fixing rising fronts, 
or for other movable parts, be either ;', in., } in., 
;°; in., or $in. in external diameter, and in pitch of 
thread and other details in accordance with the 
generally recognised Whitworth standards for 
these sizes. 


CAMERA STAND (Ftr., Pied; Ger., Stativ) 


A raised support for the camera, to keep it 
steady during focusing and exposure. There are 
several varieties, differing 1n construction accord- 
ing to their purpose. In the older but still very 
common form of studio camera stand B the top 
is raised or lowered by rack and pinion, or by 
a counterpoise and weight, while the table has a 
tilting movement. The better class of studio 
stand is, however, much more ornate and elabor- 
ate (see ““Studio Camera’’). The Hana studio 
stand C is novel in construction, having a counter- 


A. Tripod Stand for Field Camera 


balanced platform travelling on two upright 
pillars, to which it may instantly be clamped 
by pulling a lever. Besides the advantages of 


Camera Stand 


ease and smoothness of movement, the camera 
may be raised as high at 7 ft. or lowered to only 
2 ft. from the ground. The tripod stand A for 


| 
‘i 
=|] f 
}) } 
iri 
4H 18 
Abd had 
H 
4 ta 
aie , 
iit 
{ 


ass 


C. Studio Stand with Counterbalanced Platform 


field cameras is usually made to fold up, the three 
legs being then strapped together for carrying. 


Camera, Vertical 


The bottom joint should have a sliding move- 
ment to allow of adjustment on uneven ground. 
The top, or head, is detachable; it is covered 


D. Telescopic Stand 


with felt to avoid scratching the camera, and it 
has a hole for the screw by which the latter is 
secuted. Many tripod legs, however, are made 
to fit a turntable at the bottom of the camera. 
The tripod head must be sufficiently large for 
the apparatus which it is to support, or vibration 
will occur. Steadiness and rigidity should be 
the distinguishing characteristics of a tripod 
stand, and should be considered before lightness, 
though the two qualities are not necessarily 
antagonistic. Telescopic stands D of brass, steel, 
or aluminium, are very portable, but are suitable 
only for light cameras. 


CAMERA, VERTICAL 

Cameras are used vertically for the purpose of 
photographing ceilings, floors, or articles laid 
upon a horizontal surface. Vertical fittings are 


A and B. Hinged and Strutted Table for 
Vertical Camera 


obtainable commercially, but most are home- 
made. A and B show a very simple arrange- 
ment, the exact size of which will depend upon 
the camera used. ‘The accessory takes the form 
of a narrow hinged table, which is screwed to the 


87 


Camera, Vertical 


ordinary tripod top, the camera being screwed 
to the hinged portion, which, in use, is supported 
vertically by a strut, as shown. The camera 
can be pointed upwards or downwards in a 
perfectly vertical position, or, if the strut con- 
tains various holes to pass over the screw, 
at any angle. The late T. C. Hepworth’s 
method (described first in 1894) allows of the 
camera being pointed downwards but not 
upwards, and it is largely used for photographing 
precious stones, medals, illustrations from books, 
etc. One advantage of such an arrangement 
(see figure C) is that it may be used in an 
ordinary room against a window, and the sub- 
jects will probably be as well lighted as in a 
studio. This arrangement has been used for 
photographing a baby lying in a cradle. The 
camera is fixed at the top end of a skeleton stand ; 
upon the glass platform E can be placed a coloured 
card, paper, or other medium to serve as a back- 
ground on which the opaque objects, flowers, 
etc., may be laid and photographed from above. 
By employing a glass platform shadows are 
obviated, and this in some cases is of great 
advantage, while at the same time it is possible 
to use at any distance below the glass a back- 
ground of any colour, which, by screening the 
light, can be lightened or darkened as may be 
required. A useful addition is a blind F to shut 
off all light from the upper surface of the plat- 
form; another is a mirror G to reflect the light 
upwards. By placing a negative upon the glass 
platform a reduced or enlarged transparency 
can be obtained more easily than by any other 
plan. Should the negative be a film it can be 
kept flat by placing a piece of glass over it. 


C. Vertical Camera 


In process work, stands holding cameras 
vertically are frequently used when copying 
small objects supported on a horizontal surface 
and these stands are also of advantage when 
copying from open books. 


Cameron, Julia Margaret 


CAMERON, JULIA MARGARET 

Born in Calcutta, 1815; died in Ceylon, 1879. 
Came to London in 1848, started photography 
in 1865, and became famous for her admirable 
portraits of celebrated persons, 


CAMPHOR (Fr., Camphre ; Get., Kampfer) 

Common camphor is known also as Japan 
camphor. A colourless, translucent, crystalline 
solid with characteristic smell; melts at 175° F. 
(nearly 80° C.), is soluble 1 in 700 of water, and 
is readily soluble in alcohol, oils, etc. It is 
used in the manufacture of celluloid, varnishes, 
and retouching mediums. Skies may be blocked 
out of a negative by holding the latter glass-side 
downwards over a piece of lighted camphor, and 
wiping away the soot from the parts of the nega- 
tive it is desired to print. 


CANADA BALSAM (Fr., Baume du Canada ; 
Ger., Canadabalsam) 

Known also as Canada turpentine. A resin- 
ous fluid, transparent, and of a greenish yellow 
tint, very viscous, and hardening into a clear 
transparent solid, whose refractive index is about 
equal to that of glass. It is obtained from the 
Balsam Fir of North America, Abies balsamea 
(Conifere). In its commercial state it has the 
consistency of honey; it may be hardened by 
exposing to the air or rendered more liquid. by 
heating or by the addition of turpentine, ether, 
or chloroform, but is insoluble in water. It 
has several uses in photography—for the cement- 
ing of lenses together, making varnishes, and 
rendering paper negatives and prints for the 
crystoleum process translucent. 

In process work, Canada balsam is used for 
sealing together the two halves of the ruled 
screens and for sealing colour filters. A further 
use is for sealing a thin microscope cover glass to 
the centre of the ground-glass focusing screen, 
so that a transparent spot is provided for 
focusing by means of a magnifying eye-piece. 


CANARY AND ORANGE MEDIUM 


A yellow or orange non-actinic fabric used for 
screening the light in dark-rooms; yellow paper 
and glass may also be used in place of the usual 
red light for some photographic purposes. It 
is less tiring to the eyes than red and gives more 
illumination. A yellow light, however, is not 
safe for modern rapid dry plates and isochro- 
matic plates, but it is admirable for bromide 
papers and lantern plates. It is more suitable 
for use with artificial light than with daylight, 
and when the latter is used two thicknesses of 
canary medium may be necessary. Orange 
medium or paper cuts off more green and blue 
light than canary medium, and allows more 
orange and red to pass, and it may therefore 
be used for the slower brands of plates providing 
the light is not particularly strong. According 
to Sir William Abney, the total illuminating 
value of the orange is nearly twice that of 
the canary. 


CANDLE BALANCE (Fr., Balance a chandelle ; 
Ger., Kerzenwage) 
An instrument employed in photometry to 
ascertain the loss of weight undergone by a 
candle after burning a given time. 


88 


Candle-light Etfects 


CANDLE-LIGHT EFFECTS 

Lighting effects in a photograph, apparently 
due to the use of a candle as the illuminant. 
Actually the candle pictured plays no part 
whatever in the real illumination of the sub- 
ject. This branch of work was made popular 
by Newson Gibson, who, during the years 
1901 to 1904, produced many remarkable 
candle-light effects which were puzzling at the 
time, as it was well known that a candle did not 
give a sufficiently actinic light for ordinary 
photography. The secret consists in using a 
piece of lighted magnesium wire hidden from 
the lens, but placed as near as possible to the 
candle flame, so that the light from the magne- 
sium appears to come from the candle, the back- 


‘ 
‘ 
4 
’ 
ie) 


Apo cnecceneed 


oe ceeme cceec oem es & wee 


(tet toes e woe mcane 


A. Magnesium Wire Holder Over Candle 


ground immediately above and behind the 
candle being quite black. A blackened holder 
supports the magnesium wire above the candle, 
and is invisible against the black background. 
Proper arrangements must be made for carrying 
off the smoke. In the illustration above,a BecD 
represents the amount of the subject taken in 
by the lens, the candle being placed as shown 
and the remainder of the picture being filled with 
suitable objects. ‘The blackened shield or tube, 
with the wire behind it, is shown at E, and is 
lowered until the wire ignites, the smoke escaping 
up the tube and not showing in the picture. 
Another arrangement B is also recommended 
by N. Gibson. A strip of wood G 30 in. long and 
1¢ in. wide is faced on the side that goes nearest 
the camera with black velvet; to the top is 
loosely fastened a long rod H as a handle for the 
operator, so that the light shield itself hangs 
vertically, whilst its weight prevents any motion. 
On the reverse side of the wooden strip is fast- 
ened a triangular chimney J made of tinplate, 
its bottom being about 14 in. from the lower 
end of the wooden strip, At the bottom of the 
chimney the magnesium kK is placed, in such a 
way that the wire may be easily lighted when 
lowered on to the candle, and the smoke may 
escape up the chimney and out of the picture. 
When the magnesium ignites, the shield is raised 
to expose the flame of the candle and the 
exposure ismade. The long chimney is necessary 
when the candle is low down in the picture, but 
when near the top and the smoke has not far 
to travel a shorter chimney may be used. 
Another worker uses a platinotype tin, as shown 
at E, one half at the bottom being cut away and 
the magnesium wire F suspended from a wire 


Candle-power 


running across the centre, the whole arrange- 
ment being suspended on wire and let down on 
the candle. It matters little what method is 
adopted as long as the magnesium is hidden 
and burned as near as possible in the position 
of the flame. ‘The flame of the candle must also 
be kept steady during the exposure. A little 
daylight may at times be used to light up the 
dark corners of the room, but it must not be 
too strong, as the light must appear to come 
from the candle itself. The necessary exposure 
can only be found by trial; as a basis for experi- 
ment, expose for the whole of the time during 
which 1 in. of magnesium wire is burning and 
after it has burnt out allow another second for 


= 
= 
= 
= 


Band C. Arrangements for Burning Magnesium 
for Candlelight Effects 


the candle flame, the stop being f/11 and the 
plate extra rapid. The “lamps” described have 
an effective radius of only 2 ft. or 3 ft., so that 
subjects must be arranged accordingly. 


CANDLE-POWER 

The unit for photometric work in England. 
The light emitted by a standard candle. (See 
* Unit of Light.’’) 


CANDLES, FLASHLIGHT 


Magnesium made up in the form of candles 
with a wick of “‘ touch’ material. The commer- 
cial candles are of various sizes, burning for and 
giving exposures up to about half a minute, the 
most popular being the 2, 4, 7, 12, and 20 
seconds sizes. The candles should be kept in a 
dry place, as otherwise they will burn and 
splutter badly when fired, and they should be 
burnt on a metal tray or iron shovel. Service- 
able flash candles of a kind may be made at 
home according to the following formula :— 


Magnesium powder 20 parts 
Barium nitrate. 0 
Flowers of sulphur ee 


Beef tallow (or suet) 7 


Melt the suet or tallow, carefully knead in the 
other ingredients, place in small metal boxes, 
mould the top to a point like that of a candle, 
and fire by means of a torch. They should be 
burnt on an iron shovel. This preparation gives 
a good light, and may be used out of doors in 
large “epoca for street work at night, and 
in small quantities in aroom. (See also “* Flash- 
light Mixtures.’’) 


) 


— 


89 


Canvas, Enlargements Upon 


CANVAS EFFECTS 


Photographs haying the appearance of being 
printed upon canvas, Negatives may be printed 
upon canvas-grained paper, which is obtainable 
commercially, or a piece of thin canvas or 
bolting cloth (which see) may be interposed 
between the negative and the sensitive paper. 
Negatives for producing canvas effects direct 
upon the paper may be obtained by exposing 
in the camera in the ordinary way, and then 
making a second exposure, this time with the 
lens focused on canvas, so adjusting the expo- 
sutes that the grain of the canvas does not pre- 
dominate over the original exposure. Another 
method is to make a separate negative of the 
canvas, and to print from this before or after 
using the same piece of paper for printing from 
another negative; this is probably the easiest 
and most economical method, as the one negative 
of the canvas may be used for any number of 
pictures, and the canvas effect printed light or 
dark over the original print as desired. A good 
strong sidelight should be used when making a 
negative from the canvas in order to emphasise 
the grain. Any suitable fabric may be substi- 
tuted for the canvas. 

In process work, @ canvas grain is often 
imparted to the highly glazed ‘‘art” papers 
used for three-colour printing, so as to give a 
more artistic effect imitating the painter’s canvas. 
This graining is done by running the paper 
between a pair of embossing rollers, one of which 
is steel, bearing the pattern, and the other of 
paper, to take the impression. 


CANVAS, ENLARGEMENTS UPON 

Enlargements are made direct upon canvas 
for the use of artists, either for finishing direct 
or as a basis for oil-colours. The canvas must 
first be cleaned with a mixture of 1 oz. of liquor 
ammoniz (°880), and 4 oz. of methylated spirit, 
this being rubbed on with a clean rag or sponge 
until all greasiness is removed. Three solutions 
will then be required for sizing, sensitising, and 
developing. 


Sizing 
Distilled water IO oz. 1,000 ccs. 
Ammonium bromide 35 gts. iy 6 
Ammonium chloride too pee 
Potassium iodide oo" 51 5 Sa 
Gelatine 600o* to 
Dry albumen FoR: 100 ,, 


Mix and warm the mixture until the gelatine is 
dissolved, but avoid overheating or the albumen 
will be coagulated. 


Sensttising 
Distilled water 6 oz. 500 ccs. 
Glacial acetic acid a 40 g. 
Silver nitrate 80 ,, 

Mix and filter. 

Developer 
Distilled water 5° Oz, 500 ccs, 
Lead acetate 5 gts. ig; 
Gallic acid #8 ie os 


The cleaned canvas is sponged over with the 
sizing mixture as evenly as possible. When 
dry it is ready for sensitising. Take the canvas 
into a dark-room, pour over it some of the silver 
sensitising mixture, and spread evenly with a 


Canvas, Mounting on 


pad of cotton wool. Wet or dry it is ready for 
exposing in the same way as bromide paper, 
but it is slower than most bromide papers. The 
developer is applied with the sponge previously 
used for sensitising, the residue of silver assisting 
development. The canvas is fixed in a bath of 
“hypo” 1 oz., water 5 oz., and washed well. 
During all these processes the canvas may 
remain on its stretcher. 


CANVAS, MOUNTING PRINTS ON 

The canvas needs to be strained on a frame. 
The print or enlargement is placed on a table 
face downwards, and coated with any good 
mountant, starch paste being as good as any- 
thing. The paste should be rubbed in well with 
the brush or sponge until the printislimp. Then 
the stretched canvas is lowered upon it, picked 
up with the adhering print, and laid right way 
up on the table. The print needs to be rubbed 
into close contact, special attention being given 
to the edges, which may need treatment with a 
paper-knife. 


CANVAS, PRINTING ON 
Printing on.’’) 


CAOUTCHOUC (See “ Indiarubber.’’) 


CAP, LENS (Fr., Bouchon; Ger., Objectiv- 
Deckhel, Linse Kappe) 

A tircular, closely-fitting covering for the 
lens, lined with black velvet. At one time all 
exposures were made by taking off and replacing 
the cap, but for this purpose a shutter is now 
commonly used. ‘The cap is still, however, often 
resorted to for time exposures; and caps are 
generally provided on stand cameras for the 
protection of the lens, even when a shutter is 
fitted behind the lens. 


CARAMEL (Fr., Caramel; Ger., Karamel) 

A deep reddish-brown, sticky liquid, made by 
heating loaf sugar. It may be obtained in 
liquid form from chemists, who call it sac- 
charum ustum, It is used in photography as a 
backing for plates to prevent halation. A rough 
and ready method of making a small quantity 
at home is to place loaf-sugar in a dry iron sauce- 
pan over a slow fire and stir with an iron spoon. 
At about 400° F. (204° C.) caramel will be 
formed, but it requires a considerable amount 
of care to make it properly, as over- or under- 
heating will spoil it. The superiority of caramel 
over other backings is due to its non-actinic 
colour and to the fact that its refractive index 
is nearly the same as that of glass. (See also 
** Backings, Plate.’’) 


CARBOLIC ACID (Fr., 
Ger., Karbolsdéure) 

Synonyms, phenylic alcohol, phenol, phenic 
acid, and hydrate of phenyl. C,;,H,OH. Mole- 
cular weight, 94. It is soluble in water, alcohol, 
ether, benzine, chloroform, etc.; it is volatile 
and extremely poisonous, and causes burns on 
the skin. It is colourless when fresh and pure, 
but gradually turns pink on exposure to light. 
It is used to preserve mountants, emulsions, and 
many other mixtures. It is the starting-point 
of many photographic chemicals. 


(See ‘‘ Fabrics, 


Acide phénique ; 


90 


Carbon Process 


CARBON BISULPHIDE (See “Carbon Disul- 
phide.’’) 


CARBON DISULPHIDE (Fr., Sulfure de car- 
bone; Ger., Schwefelkohlenstoff) 

Synonym, carbon bisulphide. CS,. Molecu- 
lar weight, 76. Solubilities, insoluble in water, 
soluble in alcohol and ether. Its vapour is 
inflammable. It is a colourless, highly refractive 
liquid with characteristic odour, which in im- 
pure samples is extremely unpleasant. Itis used 
as a solvent for unvulcanised indiarubber in 
making rubber solution. 


CARBON ENLARGEMENT 

An enlargement made by the carbon process. 
As this process of printing is much too slow for 
making direct enlargements in the camera, an 
enlarged negative has to be made, and prints 
taken from that by daylight in the ordinary 
manner. For printing in carbon, an enlarged 
negative should be reversed, so that the print 
can be made by the single transfer method and 
still be non-reversed. The most simple and 
satisfactory manner of obtaining a reversed 
negative when reproducing or enlarging is to 
reverse the transparency in the carrier, putting 
the glass side towards the lens instead of the 
film. (See also “‘ Enlarged Negatives” and 
** Carbon Process.’’) 


CARBON PROCESS 

The idea of the carbon process as it is known 
to-day is credited to A. L. Poitevin, who, in a 
patent dated December 13, 1855, describes 
the action of light upon a chromated gelatine 
mixed with a pigment. J. Pouncy is supposed 
to have been the first actually to produce carbon 
prints, his patent being dated April 10, 1858. 
In these early processes the half-tones were 
mostly unsatisfactory, and modifications were 
made by J. C. Burnett (1858) and Fargier (1860) ; 
but it was not until J. W. Swan’s improvement 
in 1864, when he patented carbon tissue, that 
the process became of any practical use to 
photographers. J. R. Johnson made further 
improvements in 1869, and in 1874 the flexible 
support used in the process was patented by 
J. R. Sawyer. } 

The earbon process differs essentially from 
all other methods of photographic printing. It 
depends for its working on the fact that gelatine, 
to which has been added a suitable proportion 
of an alkaline bichromate, becomes insoluble 
when exposed to light, but retains its solubility 
if kept in the dark. A sheet of paper is coated 
with a mixture of gelatine, colouring matter, and 
potassium bichromate, and then exposed to day- 
light under a negative. The portions of the 
gelatine film that were protected by the high 
lights or dense parts of the negative retain their 
solubility, while those that receive the full force of 
the light through the shadow portions become 
insoluble. Parts exposed under the intermediate 
tones become partially soluble. By treating the 
film with hot water the soluble portions are dis- 
solved away, while the insoluble parts remain, 
and form the picture. Any colouring matter 
may be employed, and consequently a picture 
may be produced in any desired colour. 

Carbon tissue is a dark-surfaced paper, the 


Carbon Process 


colour corresponding to the deepest tone that 
can be obtained in the picture. No visible 
image is produced by exposure to light, and 
consequently, the exposure in the printing frame 
must either be timed or gauged by an actino- 
meter. Carbon tissue sensitised in H. ; 
Bennett’s sensitising bath requires about half 
the exposure necessary for printing-out silver 
paper to the full depth necessary for toning, 
or rather less than the printing-out paper 
requires to give a visible image resembling a 
finished result. The prints should be developed 
as soon as possible after taking from the frame 
(see “ Continuing Action”). A piece of single- 
transfer paper, slightly larger than the exposed 
print, is also required. The exposed film must 
be developed from the back, for the reason that 
the whole of the face has been rendered insoluble, 
excepting the extreme high-lights, while all the 
surface in contact with the paper has remained 
soluble. The film is so thick that the strongest 
shadow does not penetrate right through. In 
the deep shadows the insolubility penetrates 
deeply ; in the medium tones there is a moder- 
ate thickness of insoluble gelatine, while in the 
very light parts there is simply a slight super- 
ficial insolubility. This layer of soluble gelatine 
of varying thickness underlying the insoluble 
image necessitates transferring the film so that 
the soluble portion becomes the surface. Any 
attempt to develop the film on its original paper 
would result in its floating right off as soon as 
the soluble gelatine commenced to dissolve. 

Transferring and developing the exposed print 
are simple matters. The piece of transfer paper 
is soaked in cold water until limp. The exposed 
print is then immersed in cold water for a few 
seconds, until it begins to become flat, and its 
face is then brought into contact with the pre- 
pared surface of the transfer paper, preferably 
under water, the two papers brought out together, 
squeegeed firmly into contact, and then partially 
dried between blotting-paper under moderate 
pressure for ten or twelve minutes. The print 
is now ready for development. It is placed in 
water that has been warmed to 105° to 110° F. 
(40°5° to 43°3° C.), and kept below the surface. 
In about twenty or thirty seconds some of the 
colour will be seen oozing from the edges. This 
is the object of the safe edge, to preserve a mar- 
gin of soluble gelatine; without it the next 
operation would be impracticable. As soon as 
the colour is seen to be oozing out, the corner 
of the paper bearing the film is lifted, and if it 
comes away easily it is pulled steadily away, 
leaving the film on the transfer paper. This film 
is allowed to soak for a few minutes in the hot 
water, and from time to time the water is 
gently splashed over it, and it is taken from the 
water and partially drained. This treatment is 
continued until the print is sufficiently light, 
when it is drained thoroughly and then rinsed in 
cold water to wash off any loose gelatine and 
colour that may adhere. It is next immersed 
for about five minutes in an alum bath (1 oz. 
to 20 oz. water), washed in about three changes 
of water, and dried. With the exception of the 
developing bath, all the solutions should be cold. 
Care must be taken to avoid touching the sur- 
face of the film during the working. 

An objection to this method of working—the 


gl 


Carbon Tissue 


Single transfer method—is that the picture is 
reversed, the left side becoming the right. When 
it is desirable to avoid this a second transfer is 
necessary, and the method is known as “‘ double 
trausfer.’’ Instead of using the single transfer 
paper, a temporary support is substituted (see 
“Flexible Support”). The method of working 
is exactly the same as described for single transfer, 
excepting for the preliminary waxing of the sup- 
port. After development, treatment in the 
alum bath, and drying the print on the temporary 
support, it is ready for the second transfer. The 
drying on the temporary support must not be 
rapid, and the transfer should take place as soon 
as possible after drying, or else the print should 
be kept in a cool place, moist rather than too 
dry. A piece of final support or double transfer 
paper is soaked in cold water for at least half an 
hour, and then the temporary support bearing 
the print is similarly soaked until quite limp. 
Both are then immersed in warm water, about 
go° F. (32° C.), for about fifteen or twenty 
seconds, face to face. Then they are withdrawn 
clinging together and squeegeed into good con- 
tact. When thoroughly dry the two papers 
may be pulled apart, and the image will be firmly 
and permanently attached to the double transfer 
paper. The necessity for the second transfer is 
frequently obviated by the employment of a 
reversed negative. (See also ‘‘ Carbon Tissue,” 
“Carbon Transfer Papers,” ‘“* Flexible Support,” 
** Bennett’s Carbon Sensitiser,” etc.) 


CARBON TETRACHLORIDE 

Synonym, tetrachloromethane. CCl, Molecu- 
lar weight, 156. A colourless, oily substance, 
resembling chloroform, volatilising completely 
without odour, having a boiling point of 170°6° F. 
(77° C.), and a specific gravity of 1°593 at 68° F. 
(20°C.), Itis obtained by acting upon chloro- 
form with chlorine, and in other ways. It has 
no action on metals, fabrics or colours, and it is 
an excellent solvent of shellac, asphalt, fats, etc, 


CARBON TISSUE 

The paper prepared for printing by the carbon 
process. It consists of a stout paper thickly 
coated with a mixture of soft, soluble gelatine 
and finely ground colour. As gelatine is colour- 
less, any suitable and permanent colouring 
matter may be employed, and this determines 
the colour of the print. In preparing carbon 
tissue, it is necessary that the film should be 
appreciably thicker than the depth of the strong- 
est shadow of the finished print in order that a 
thin layer of soluble gelatine should remain 
between the insoluble shadow and the paper 
support. Carbon tissue is prepared in two forms, 
sensitive and insensitive. In the former, a 
certain proportion of potassium bichromate is 
mixed with the gelatine and colour when pre- 
paring the film; in the latter, the bichromate is 
omitted, and the tissue requires sensitising by 
immersion in a bath of potassium bichromate 
before it can be used. 

In process work, carbon tissue is used to a 
considerable extent, the photogravure process 
being; for example, solely worked with a carbon 
resist developed on the copper plate. The 
special autogravure tissue is generally employed, 
but some workers prefer the ordinary standard 


Carbon Transfer Papers 


brown. It is also used as the resist in engraving 
copper rollers for the rotary intaglio process of 
printing. It may also be used as a resist for 
relief grain blocks (an inverted photogravure). 
In the Government Survey Offices an electro- 
typing process for the reproduction of maps is 
worked by developing a carbon print on a silvered 
copper plate, and then depositing copper on it 
so as to form a duplicate plate. 


CARBON TRANSFER PAPERS 


Transfer papers for receiving the film or 
image in the carbon printing process. Two 
kinds of such paper are used, called respectively 
“single transfer paper’’ and ‘‘ double transfer 
paper.’’ The former are those employed when 
the film or image is transferred from its original 
paper to one on which it is to remain perma- 
nently; the latter are used when the film is 
transferred to a temporary support for develop- 
ment, and re-transferred to a fal support as its 
permanent basis. Single transfer paper is pre- 
pared by coating any suitable paper with gela- 
tine that has been so ee as to be prac- 
tically insoluble and impermeable. Double trans- 
fer paper bears a thicker coating of soluble 
gelatine. Both kinds of paper are easy to 
prepare; any carbon worker can _ therefore 
obtain his favourite paper by preparing it 
himself. 

The easiest method of working for the single 
transfer process is to coat the paper first and 
harden the gelatine coating afterwards. A 
solution of gelatine should be prepared, 1 oz. 
being soaked until soft and then dissolved by 
heat and made up to about 25 oz. The gela- 
tine solution should be applied to the paper as 
evenly as possible, by means of a flat brush or 
aspouge. The brush should be taken first along 
the sheet of paper, then across, and then diagon- 
ally, so as to avoid ridges and to render the 
coating even. Many workers prefer to give two 
thin coatings rather than one of medium thick- 
ness, the second being applied after the first 
is quite dry. When the gelatine coating is 
thoroughly dry it should be hardened by immers- 
ing the prepared paper in a solution of chrome 
alum, 12 grs. to each I oz. of water. Three or 
four minutes should be allowed for immersion, 
and the paper should then be rinsed in two or 
three changes of water and dried. 

For double transfer a thicker coating of 
gelatine is required, this being obtained by 
two or three coatings of the solution given 
for single transfer; and no hardening solution 
is employed. Both kinds of paper will keep 
indefinitely if stored in a dry place. The 
methods of using are given under the heading 
*“Carbon Process.” 

The double transfer paper is often used by 
photo-lithographers as a photo-transfer paper, 
and is found to be very suitable for this purpose 
.when sensitised with bichromate. 


CARBONATE 


A salt derived from the hypothetical dibasic 
acid H,CO;, or carbonic acid; for instance, 
Na,CO, carbonate of soda. Carbonates are of 
three kinds, normal, acid, and basic; all are 
decomposed by dilute sulphuric or hydrochloric 
acid, with the production of carbon dioxide. 


92 


_ Caricature 


CARBOXYLIC ACIDS 


Acids derived from the aromatic hydrocarbons 
by the substitution of one or more carboxyl 
groups (COOH) for a corresponding number of 
hydrogen atoms; they are named mono-, di- 
carboxylic acids, etc., accordingly. Examples 
are formic and acetic acid. 

Hydroxycarboxylic acids are carboxylic acids 
containing also a hydroxyl group (OH). An 
example is lactic acid. 

Amido-carboxylic acids contain the amido or 
amino group (NH,) as well as COOH. 


CARCEL LAMP (Fr., Lampe carcel ; 
Carcel-lampe) 

A lamp adopted at the Paris Electrical Con- 
gress of 1881 as the French unit of illumination 
in photometry. It burns 42 g. of colza oil per 
hour, has a flame 40 mm. in height, and gives a 
light equal to about 9} standard candles. 


CARICATURE (Fr., Caricature; Ger., Zerrbild, 
Kartkatur) 


A freak portrait obtained by using special 
backgrounds and foregrounds, distorting the film, 
copying, etc. Some of the methods of producing 
caricatures are described below, and others will 
be found under such definite headings as 
‘*“ Doubles’ and “‘ Trick Photography.” Large 
heads on small bodies.—These may be produced 
in many ways, one of which is to draw the neces- 
sary figure, without a head, upon a sheet of 


Ger., 


A and B. Caricature Cards 


white cardboard, the collar, or neck, being at the 
extreme top, as at A, or a circle may be cut out 
for the insertion of the head, as at B. If the 
former is used, the model sits upon a chair and 
holds the design under the chin. The bark- 
ground should be of the same colour as the 
caricature card, and the junction between the 
two is spotted out so as not to show upon the 
finished print. An objection to the above plan is 
that only the head of the sitter is photographed 
and the following method may be preferable: 
Two negatives, one of the head of the size re- 
quired and one a smaller picture of the body, 
are made; the larger head is cut from the print 
and pasted over the smaller head in the other 
picture, the whole being then copied in the 
camera. Distorted heads and bodies.—Distorted 
images may be obtained by warming a partially 
dried negative before a fire or over a gas flame, 
the heat causing the gelatine to melt ; the picture 
can be made to “run,” and can be distorted, 
therefore, to any extent. When dry, the nega- 
tive can be printed from in the usual way; but, 


Carmine Tones 


of course, it cannot be restored to its original 
state. Another plan is to strip the film from 
the negative, and to attach it to another glass, 
stretching it during the process, and allowing it 
to dry in its stretched position upon the new 


C. Obtaining Thin-face Caricature 


support. Broad and long faces.—Excessively 
long or broad faces may be produced by the use 
of convex or concave mirrors. The sitter is posed 
in front of the mirror, and the distorted image 
in the glass photographed; but great care is 
necessary to avoid reflections. Another, and a 
much easier, plan is to copy an existing and 
proper photograph; for example, the portrait 
print is placed in front of the camera, with one 
edge nearer to it than the other, asin C. The 
result will be that the width of the face is partly 
lost, the effect being a lengthening of the face. 
If an excessively broad face is desired, the print 
is copied while lying at an angle to the horizontal 
plane (the less the angle the shorter will be 
the resulting figure); D shows the idea, the 
bottom edge of the picture being nearer to the 


- 
_ 
—_—_— 


ea 
—__— 
ers ey 


D. Obtaining Broad-face Caricature 


camera than the top edge. Many firms sell 
specially painted comic backgrounds for making 
caricatures, also negatives of comic scenes into 
which the head from any existing negative can 
be printed. 


CARMINE AND CRIMSON TONES 

If a negative is of good contrasts P.O.P. 
prints from it may be toned to a good carmine, 
as follows: Print and wash as usual, and tone 
in— 


Ammonium sulpho— 


cyanide . ; 620. 8a, 452 
Potassium iodide Stead amen 9:55 
Gold chloride . ser, UA ae 
Water : . A 32 0Z.:; oF,OGO" ces. 


Toning takes from twenty to thirty minutes, 
and the tone as well as the time may be altered 
by varying the amount of iodide. The bath has 
a slight intensifying action. Any discoloration 
on the back of the paper and in the high lights 
will disappear in the fixing bath. Wash and 
fix in “hypo” as usual. 


93 


Casein 
CARRAGEEN (See “ Iceland Moss,’’) 
CARRIER (See “Camera Carrier,” ‘‘ Plate 


Carrier,’”’ etc.) 


CARTE-DE-VISITE (Fr.) 

A popular size of professional studio portrait. 
Size of mount, 44 in. by 24 in.; size of print, 
3$ in. by 2} in. or 3% in. by 2% in., the latter 
being “* No. 1 C. de V.,”’ and the former “‘ No. 2 
C. de V.” The carte-de-visite was at the height 
of its popularity in England in the sixties of 
the nineteenth century. Its origin was due to a 
fancy of the Duke of Parma, who, in 1857, had 
his portrait gummed on his visiting-cards in the 
place of hisname. Ferrier, a professional photo- 
grapher of Nice, is supposed to have produced 
the first of this popular size; but it was Disderi, 
of Paris, the Court photographer to Napoleon 
III., who made it popular. 


CARTON DURA 

Hard waterproofed cardboard, formerly used 
for making photographic dishes. It was made 
by coating Bristol board with linseed oil, varnish 
and asphalt, but has now been superseded by 
papier maché. 


CARTRIDGE FILM (Fr., Peilicule enroulée ; 
Ger., Patronfilm) 

A daylight-loading roll-film, consisting of an 
emulsion on paper or celluloid, wound on a 
wooden spool, together with a length of opaque 
black paper. Cartridge films are used in roll- 
holders—a kind of dark-slide—and in various 
forms of hand cameras made to take the films 
direct. A winding key is employed to pass the 
film, as exposed, on to another spool. The first 
roll-film on a paper support was introduced, in 
1875, by L. Warnerke, and the first celluloid 
roll-film in 1889, by the Eastman Company. The 
non-curling film—that is, a celluloid film with a 
thin layer of plain gelatine on the back—was 
placed on the market by the latter firm, now 
known as Kodak, Ltd., in 1903. 


CASEIN, OR CASEINE (Fr., Caséine; Ger- 
Kasein) 

Solubilities, insoluble in water, soluble in 
alkalis and organic acids. It is obtained from 
milk by acidification, and is commonly known 
as curds. It has been introduced as a vehicle 
for the silver salts in printing-out paper, as it 
gives a film which does not become sticky, does 
not curl up, and is not easily scratched. 

In process work, caseine has been advocated 
for some years past by Prof. Namias and others 
as a substitute for albumen and fish-glue enamel 
to form a resist for etching zinc or copper. It 
has not, however, come into general use. The 
casein solution is made up as follows :— 


Liquor ammoniz ; 34 OZ. 
Potassium carbonate “ ns @ 
Caseine . ? ; ‘ nae ee 


Allow the whole to stand some hours to dis- 
solve, and sensitise the solution with a saturated 
solution of ammonium bichromate. The whole 
is mixed and filtered into a clean bottle, which 
has to be kept closed. The plate is coated in 
the usual way, and after exposure under a 


Caseine Pigment Printing 


negative is inked and then immersed in water. 
Afterwards it is rinsed without rubbing with 
cotton-wool. The caseine image is highly resist- 
ant to the mordants usually employed, without 
the necessity of burning-in. 


CASEINE PIGMENT PRINTING (Fr., Tir- 
age en caséine et pigment; Ger., Kasein 
Pigmentdruck) 

A process patented by the Neue Photograph- 
ische Gesellschaft, in 1908, for obtaining prints 
in caseine and pigment from bromide or other 
silver prints. The caseine is employed either 
in the form of ‘“‘ curd,” or in an acid or alkaline 
solution. In a typical formula, 2,200 grs. of 
pressed-out curds and 440 to 520 grs. of water- 
colour are ground together, the mixture being 
brushed over the bromide print and allowed to 
dry. The print is then immersed for ten to 
fifteen minutes in :— 


Potassium bichromate . 88 grs. 9 g. 
Potassium ferricyanide . 88 ,, Obs 
Potassium bromide S eorti. Fy, 


Water to 


This has the effect of rendering the pigment- 
incorporated caseine insoluble at those parts 
where the silver image is present, the action 
varying in degree according to the depth or 
gradation of the latter. The picture may there- 
fore be developed in water at from 105° to 
125° F. (41° to 51° C.), after the fashion of a 
carbon print, a little potassium oxalate or 
sodium bicarbonate being added to ensure 
clearness of the lights. The original black silver 
image fades to a faint brown during treatment, 
and is practically invisible under the final pig- 
mented picture. 


CASKET LENSES 


In their original form casket lenses were put 
upon the market by Darlot, of Paris. His set 
consisted of a portrait lens (covering 7 in. by 
6 in., or with a smaller stop and adjustment of 
the tube 84 in. by 64 in.) and six single achro- 
matic lenses fitting into the same tube, which 
could be used alone or in pairs, giving fifteen 
double lenses varying in focal length from 24 in. 
to 9 in., each covering a plate whose length is 
considerably greater than the focal length of 
the lens. Other makers have since produced 
similar sets, amongst them being caskets of 
simple uncorrected “‘spectacle”’ lenses for artistic 
photography. The highest development of the 
casket idea is found in the Zeiss Satz-anastigmats. 
These consist of three or four perfectly corrected 
anastigmatic lenses working at f/12:5. The D 
set gives, in the single combinations, focal lengths 
of 114 in. to 19 in., and as doublets four com- 
binations working at /f/6°3, the focal lengths 
varying from 7 in. to 10 in. The casket system 
was very popular some years ago. 


CASSETTE (Ger., Kassette) 


A French term occasionally used in early 
British photographic works, and meaning the 
plate-holder or dark-slide, 


CASTILE SOAP 


A pure soap made from olive oil and soda, 
and obtainable in two varieties, one a pure white 


20 1,000 ccs. 


»? 


94 


Catatype 


or yellowish white, and the other marbled or 
veined with bluish-green; the former is the 
better for photographic purposes. It is used for 
making encaustic pastes or for waxing glasses to 
be used for stripping, also, when mixed with 
methylated spirit, as a lubricator for prints to be 
passed through a bar burnisher. 


CASTOR OIL 
Rizinusél) 

Solubilities, insoluble in water, soluble in 
alcohol, ether, and glacial acetic acid. It is a 
pale yellow, non-drying oil, obtained by expres- 
sion from the seeds of Ricinus communis. It is 
used in some varnishes and enamel collodion, 
and to render paper translucent. Also, it is 
used for temporarily cementing lenses, and as a 
lubricant. 

In process work, castor oil is used in two very 
useful ways. It is added to collodion to make 
it more flexible for the stripping process, and it 
is used for treating the surface of an albumen 
or fish-glue coating on zinc or copper, so as to 
cause a negative film to adhere temporarily 
whilst printing is in progress. 


CATALYSOTYPE (Fr. 
sotypie) 

A variation of the calotype process, invented 
in 1844 by Dr. Woods, in which the paper is 
coated with a syrupy mixture containing 
ferrous iodide instead of with potassium iodide. 
The coated paper, having been sensitised by 
brushing over with a silver nitrate solution, is 
exposed in the camera, and the image either 
develops itself, or is caused to appear by merely 
keeping the paper moist. Its name was given 
under the erroneous impression that the develop- 
ment was due to a catalytic action—that is, a 
chemical change brought about by an agent which 
remains itself apparently unaffected. It is now 
known, however, that this is not the case, since 
ferrous nitrate, an energetic developer, is pro- 
duced when the paper is treated with the silver 
nitrate solution, by the same decomposition that 
forms the sensitive silver iodide. The process 
is not very satisfactory, the silver solution being 
soon blackened by the iron, and the ferrous 
iodide mixture itself being inconstant in com- 
position. 


CATATYPE (Fr. and Ger., Catatypie) 

A process depending on catalytic action, which 
is defined in the preceding article. In the 
original catatype process patented by Messrs. 
Ostwald & Gros in 1901, a negative image 
consisting either of silver or platinum is immersed 
in a solution of hydrogen peroxide in ether, being 
then withdrawn and the ether permitted to 
evaporate. The peroxide is decomposed where- 
ever it comes in contact with the metal, but in 
various degrees according to the different grada- 
tions of the picture. The negative so treated is 
now pressed into contact with a _ gelatine 
film for a few seconds, an invisible hydrogen 
peroxide image being thereby taken up by the 
latter. If the gelatine film is then immersed in 
an alkaline solution of a manganous salt, brown 
manganese peroxide is formed wherever hydrogen 
peroxide is present, a brown positive image 
being thus obtained. Or, if an alkaline silver 


(Fr., Hutle de ricin; Ger., 


and Ger., Cataly- 


by 


acd 


PP eis, 


Catechol 


solution is used instead of a manganous salt, 
a black image in metallic silver results. 

Another method is to place an ordinary 
negative in contact with hydrogen peroxide, as 
before, and to bring it for about thirty seconds 
into contact with a gelatine paper in which a 
pigment is incorporated, the paper being then 
immersed in a solution of a ferrous salt. The 
invisible hydrogen peroxide image taken up by 
the gelatine will oxidise the ferrous salt to the 
ferric state, in which it is able to render the 
gelatine insoluble, the insolubilisation exactly 
corresponding to the various degrees in which 
the peroxide is present. The print can then be 
developed with warm water, as in the carbon 
process. There are many other variations of 
the catatype process, mostly patented. 


CATECHOL 
Another name for the pyrocatechin developer. 


CATECHU OR CUTCH (Fr., Caiechou ; Ger., 
Katechu) 

Solubilities, soluble in water and alcohol. It 
occurs in irregular, brittle masses of dark brown 
colour, slightly porous and glossy when freshly 
broken ; it is an extract obtained from the wood 
of a species of acacia. 

There are several varieties of catechu known 
in commerce, the principal being ordinary or 
brown catechu, yellow lump catechu, and cubical 
or yellow catechu, but all are of practically the 
same composition. Bengal or Bombay catechu, 
of the ordinary or brown variety, is the best 
for photographic purposes, it being rich in 
tannin. It is of a dark reddish-brown colour 
with a brilliant fracture, and is almost entirely 
soluble in water, giving a highly coloured brown 
solution. It is used for toning platinum prints, 
the process being known as “‘ Packham’s,”’ also 
for toning blue (ferro-prussiate) prints-to a green- 
ish-black colour, the latter being known as Roy’s 
process. (See “ Blue-print Process.’’) 


CATECHU TONING 

A method of toning prints on platinum paper 
to various shades of brown by means of a solution 
of catechu was introduced by J. Packham in 
1895. ‘The stock toning solution is made up as 
follows: Place 120 grs. of catechu in 5 oz. of 
water and boil for five minutes; allow to cool, 
and then add 1 oz. of alcohol. To make up a 
working solution add 30 to 40 drops of the stock 
solution to one pint of water, and heat to a 
temperature between 130° and 150° F. (54° to 
66° C.). The washed black and white platinum 
pictures are immersed therein, and toning wil 
be complete in about fifteen minutes, the colour 
being a rich mellow brown. Within one minute 
of immersion the prints will probably begin to 
change, and thereafter pass through various 
shades of brown in succession; immediately 
the desired brown is reached, the print is put 
into cold water which at once stops the toning 
action. A few minutes’ washing completes the 
operation. When the water with which the 
toning bath is made contains a considerable 
amount of lime, the solution becomes pink and 
slightly stains the whites of the picture. This 
may be counteracted by adding 2 grs. of potas- 
sium oxalate to each pint of the toning bath, the 


95 


C.C. 


addition tending to give tones of a warmer 


colour. J. Packham also states that after 
toning with catechu and washing, the per- 
manency and brightness of the image are aided 
by immersing the print for about five minutes 
in a solution of very weak potassium bichromate 
of a light straw colour. The prints must not be 
allowed to remain too long in the catechu toning 
bath, or the whites will be degraded, as the 
process is really that of staining. If desired, the 
bath may be used cold, in which case toning is 
very slow indeed. As the catechu-tannic acid 
in the catechu combines to form an inky com- 
pound with iron, it is important that the latter 
be entirely removed from the prints before toning. 
Chapman Jones has stated that catechu toning 
is due to the action of the extract upon the iron 
compound left in the print, which it is difficult, 
if not impossible, to remove completely, and 
that other substances which give colours with 
iron salts would give similar results, though 
perhaps not such desirable colours. The fact 
that the image is toned appears to be due to the 
fact that platinum holds the minute residue of iron 
more tenaciously than the paper alone, and that 
the residual iron compound is therefore roughly 
proportional to the thickness of the platinum 
deposit. (See also “* Platinotype Process.’’) 


CATHODAL RAYS 
graphy.”’) 


CATHODOGRAPHY AND CATHO- 
GRAPHY 

Names at one time given to radiography, or, 

as it is more commonly called, “‘ X-ray’ photo- 


graphy. 


CATOPTER (Fr., Catoptron ; Ger., Katopier) 

An optical instrument in which reflection is 
made use of; a mirror. A concave mirror was 
employed by some of the early Daguerreotypists 
instead of a lens. 


CAUSTIC (Fr., Caustique ; Ger., Atz) 

Synonyms, hydroxide or hydrate. Caustic 
compounds are those in which it may be con- 
sidered that a metal has replaced one of the 
hydrogen atoms in water, thus H,O = water, 
KHO = potassium hydrate, or caustic potash, 
NaHO= sodium hydrate, or caustic soda, 
CaHO = calcium hydrate, LiHO = caustic 
lithia. They are all powerful alkalis. Caustic 
potash and soda are used in some developers as 
accelerators, especially with hydroquinone, but 
must be employed sparingly as they tend to 
cause frilling. 


CAUSTIC LITHIA 


(See ‘‘ X-ray Photo- 


(See “‘ Lithium Hydrate.’’) 


CAUSTIC POTASH (See “ Potassium 
Hydrate.” ) 
CAUSTIC SODA (See ‘Sodium Hydrate.’’) 


C.C. 

Cubic centimetre, a measure used in the 
metric system. The English equivalent is 
17 minims (nearly), or -035 fluid ounce. 

C.C. is also used to indicate coilodio-chloride 


paper. 


Cedar Oil 


CEDAR OIL (Fr., Huile essentielle de cédre ; 
Ger., Zedernholzél) 

Synonym, oil of red cedar wood. A yellowish, 
volatile liquid with pleasant odour, obtained 
from Juniperus virginia, and other species of 
cedar, It is used in microscopy as a clearing 
agent and with oil immersion lenses. 


CELESTIAL PHOTOGRAPHY (Fr., La 
photographie astronomique ; Ger., Astrono- 
mische photographie) 

This is described fully under the heading 

““Cosmical Photography.” 


CELLOIDIN (Fr. and Ger., Celloidin) 

Solubilities, insoluble in water, soluble in a 
mixture of alcohol and ether. A specially pure 
form of pyroxyline (which see), made by 
Schering. Usually it occurs in the form of thin, 
yellowish, transparent shavings. 

In process work, celloidin is largely used by those 
who make up their own collodion. The sub- 
stance comes on the market either in large dry 
flakes or in small dry chips, or in chips moist- 
ened with alcohol. It is used in the proportion 
of from 1 to 2 per cent. 


CELLS, LENS 


CELLS FOR MICROSCOPICAL SPECI- 
MENS 

Cells for mounting preserved specimens or 
sections in glycerine, etc., are made by tracing 
a circle of Brunswick black on a glass slide and 
attaching a cover glass. 

In the photo-micrography of living objects one 
of the most convenient materials for cell making 
is plasticine; a small piece of this is rolled out 
between the hands, bent into a circle, placed on 
the glass slide, and flattened out by pressure with 
another glass slide, until the cell is of the required 
depth. The cell is filled with water and the 
object placed inside; then a cover slip pressed 
down keeps the liquid in the cell. Another 
common form of cell for living objects is an 
indiarubber ring cemented by Canada balsam or 
rubber solution to the glass slide, a cover glass 
being placed on top when the object is in position. 


CELLULOID (Fr. Celluloide ; Ger., Cellulozd) 

Solubilities, insoluble in water, soluble in 
acetone, alcohol, and ether. It is obtained by 
casting on metal cylinders a viscous solution of 
pyroxyline (which see) in naphtha, amyl acetate, 
fusel oil, and camphor in varying proportions. 
This gives the thin sheets used in roll-film 
cameras, and the thicker strips used in kinemato- 
graphy. Thick sheet celluloid is usually obtained 
by casting the celluloid in blocks and shaving 
off to the required thickness. Its principal use 
is for the support of films of all kinds and for 
making celluloid varnish or zaponlack. 

A great objection to celluloid is its inflamma- 
bility. A non-inflammable variety (see “ Cellu- 
lose Acetate’’) has been placed on the market. 

A formula for a celluloid varnish is:— 


(See ‘“‘ Lenses, Brasswork of.’’ ) 


Celluloid or pyroxyline 90 gts. 6 g. 

Acetone : A - 1Iodrms. 35 ccs. 
Amyl acetate ° o Le cee es 
Benzole . ° 6 200 aro oe 


96 


Cementing Lenses 


Old and spoilt films with the gelatine cleaned 
off will provide the celluloid; more or less is 
used to regulate the consistency of the varnish. 

In process work, a celluloid varnish made by 
dissolving celluloid in acetone is sometimes 
used as a substitute for stripping collodion. The 
celluloid solution is flowed over the negative, 
after the application of rubber solution. 


CELLULOID, CEMENTS FOR 

The best cement for celluloid is a solution of 
celluloid in amyl acetate or acetone. In joining 
a kinematograph film, for example, the two ends 
are scraped thin, lightly coated with cement, 
and placed between glass plates to dry; grease 
on the glass will prevent the pressed-out cement 
adhering to the glass. Many other cements are 
available for mending broken celluloid goods. 
A solution of 1 part of shellac in a mixture of 
I part spirit of camphor and 3 to 4 parts of alcohol 
(90 per cent.) will answer; as will also a marine 
glue consisting of pure indiarubber, shellac, and 
naphtha. Canada balsam may also be used in 
the form of a solution in benzine. 


CELLULOSE (Fr., Cellulose ; Ger., Zellulose) 
(CgH1905)x, Molecular weight, (162),, Ob- 
tained from the cell walls of plants and usually 
in the form of cotton-wool, which is the material 
from which cellulose acetates and nitrates are 
made. : 


CELLULOSE ACETATE (Fr., Cellulose acé- 
tate; Ger., Celluloseacetat) 

(CgHi005) 3COOH. This is obtained by the 
action of acetic anhydride on cellulose, usually in 
the form of cotton or cotton-wool, in the presence 
of glacial acetic acid and some condensing agent 
such as sulphuric or phosphoric acids or acetyl 
and zinc chlorides. ,The cotton may be mer- 
cerised or not, or previously converted into hydro- 
cellulose, or the hydrolising may be effected in 
the acetylising bath. It occurs as a granular 
powder of white or faintly yellowish colour, or 
in the form of the original cellulose itself. It is 
of special interest, as it forms the basis of the 
non-inflammable celluloids that have been placed 
on the market. Films prepared with it fuse 
and char, but will not burn. It is insoluble in 
alcohol and ether, and nearly all the solvents of 
pyroxyline, but soluble in phenol, tetrachlor- 
ethane and alcohol, acetone and alcohol, etc. 


CELLULOSE NITRATES (See “ Pyroxyline.’’) 


CELLULOTYPE 
Etching on celluloid with the needle point for 
intaglio printing. 


CELLUTYPE 
Printing blocks cut in celluloid with the object 
of superseding woodcuts. 


CELSIUS THERMOMETER (See “ Thermo- 
meter.’’) 


CEMENTS (See ‘“‘ Mountants’” and various 
substances, ‘‘ Ebonite,’’ ‘‘ Glass,”’ etc.) 


CEMENTING LENSES (See ‘‘ Lenses, Cement- 
ing.” ) 


ssad01d ANO][Od-1n0J sy} Aq paonposdar puB ‘avid smMOIYIIdoOIG AvjnC] 9Y} VO USHB} *SANOjoOo [eAnjBU UT ydeisojoyd y 


AAIT TVILS 


Centigrade Thermometer 

CENTIGRADE THERMOMETER (See 
“* Thermometer.’’) 

CENTIGRAM, CENTIMETRE, CENTI- 
LITRE, ETC. (See “Weights and 
Measures,.’’) 

CENTRAL SPOT (See “ Fiare.’’) 

CENTRE OF ADMISSION (See “ Nodal 


Points.’’) 


CENTRIFUGAL SEPARATION (Fr., Sépara- 
tion centrifuge; Ger., Separiven mittels 
einer Lentrifugalmaschine) 

A method introduced by Plener in 1881 for 
separating the sensitive silver salts from the 
gelatine used during the manufacture of emulsions, 
The fluid emulsion is poured into a gunmetal 
receptacle, which is rotated at a speed of from 
4,000 to 6,000 revolutions a minute, the silver 
salts being thrown on to the walls of the con- 
tainer, whilst the gelatine and water escape by 
an orifice at the bottom. It is claimed for this 
method that the emulsion is very rapidly freed 
from the nitrates, formed as by-products, and 
the decomposed gelatine. The method has fallen 
into almost complete desuetude. 


CENTRING OF LENSES 

When a lens is correctly centred the axes of 
all its surfaces are in a straight line; otherwise, 
good definition cannot be obtained. Faulty 
centring gives a distortion to the image similar 
to that of astigmatism or coma, and is easily 
detected by fixing the lens upon a camera or 
optical bench and focusing a brightly illuminated 
object, such as a small lamp flame or mercury 
bulb. The position of the image is carefully 
noted, and the lens gently rotated in its flange, 
when, if the centring be perfect, the image will 
remain quite stationary, but if not it will move 
in more or less of a circular direction upon the 
screen. The fault may be in the flange, or rather 
the body ring of the lens tube, or it may be in 
the thread upon the lens cells, in the cementing 
of the separate components, or the surfaces of 
one or more of the single glasses of the combina- 
tion may not be correctly adjusted. In any case, 
it is a matter for an experienced optical work- 
man to put right. 

The centring of the actual components of the 
lens is a sore process, but one requiring con- 
siderable skill, When a lens leaves the polisher’s 
hands it has a more or less rough edge, and is a 
little larger than the cell it is destined to fit. It 
then goes into the hands of a workman for 
“edging” and “centring,” which operations 
are performed simultaneously. The lens is 
stuck with pitch upon a revolving chuck, and a 
gas flame is so adjusted that two images of it 
are seen by reflection from the inner and outer 
surfaces of the lens. These will be found to 
‘‘ wobble’ as the lathe head rotates, and the 
workman slides the lens upon the soft pitch until 
they are quite steady. The pitch is then allowed 
to set and the edge of the lens is ground to correct 
size upon the lathe by the application of a copper 
plate fed with wet emery powder. A similar 
process is gone through after cementing two or 
more glasses together while the balsam is suffi- 

7 


97 


Ceramic Process 


ciently soft to allow the surfaces to be moved 
upon each other. 


CERAMIC PAPER 


A paper at one time used for the production 
of ceramics; invented by Guerot in 1891. It 
was sensitised with a solution the constituents 
of which were kept a trade secret. The paper 
was printed upon, washed, squeegeed in contact 
with the vitrifiable plaque, and stripped. The 
image was then treated with a solution of potas- 
are permanganate, washed, dried, and finally 

red. 


CERAMIC PROCESS 

The art of obtaining a burnt-in impression of 
a photograph on earthenware, china, or porcelain. 
Such pictures are permanent because the image, 
formed by a vitrifiable powder, is protected by 
an imperishable glaze. The material of which 
the picture is composed must obviously be of a 
special nature. The process is based on the 
dusting-on or powder process, in which a bichro- 
mated film loses its tackiness in different degrees 
by exposure to light under a negative, so that 
on brushing it over with a suitable powder an 
image is obtained ; but in ceramic photography 
the powder used is a vitrifiable colour which 
stands firing without injury. 

The transparency used must be bright, vigor- 
ous, and of the highest quality. The image for 
firing is not produced at first on its final support. 
A polished glass plate forms a temporary sup- 
port, the print obtained on it being afterwards 
coated with collodion, stripped and transferred. 
The glass plate is cleaned and coated with a mix- 
ture of the following two solutions :— 


Organtfier 
Le Page’s fish-glue : 2 OZ; 62 g. 
Glucose ‘ : Si als eg A 
Glycerine F : J 260s. i 12 ccs, 
Water ° ° Peas Oz. 600 ,, 
Sensitiser 
Ammonium bichromate goo ers. 58 g. 
Water... . ; 21 OZ. 600 ccs. 


If a smaller quantity is desired, keep to the 
same proportions. Mix together in equal parts 
and filter as required. Such solutions may be 
purchased ready prepared. The coated plate is 
dried by gentle heat, not greater than that which 
can be borne comfortably by the back of the 
hand. A whirler is useful for rapid drying. A 
thin, even coating should be aimed at, and the 
film ought to be quite glossy when dry. The 
exposure under the transparency varies with the 
quality of the latter and the light, and it is better 
to use an actinometer; it may range from forty 
seconds to three minutes in the sun, or to as 
much as fifteen minutes in diffused light. With 
a correct exposure the image will be faintly 
visible on the film. Development is performed 
as in the dusting-on process (which see), but 
the plate is held in an inclined position resting 
on a sheet of white paper, sensitive side towards 
the light, so that progress may be viewed by 
both transmitted and reflected light ; and vitri- 
fiable powders must be employed. These con- 
sist of metallic oxides and other fusible sub- 
stances, and they are obtainable in a number of 


Ceramic Process 


different tints. Sift the powder through silk, 
but it may be necessary, before doing this, to 
re-grind it with water, using a muller on a glass 
slab. The powder must be thoroughly dried 
before sifting. Firing alters the colours of the 
powders to an extent that only experience will 
show. When the image possesses about the 
same vigour and transparency as a good lantern 
slide, the surplus powder is dusted off, and the 
picture coated with collodion (either plain or a 
special preparation), which is flowed over the 
plate like a varnish. When the collodion has 
set, a sharp penknife is pressed downward 
through the edges of the film on three sides of 
the plate, cutting through to the glass; the plate 
is then immersed in several changes of water, 
preferably filtered, to remove the bichromate 
salt. The film will separate from the plate, 
except on one side. When the bichromate seems 
nearly all removed, the film is placed in a solu- 
tion of fused borax for about ten minutes, 
finally washing in a fresh bath of filtered water 
for an equal period. To prepare the fused 
borax solution, place 2 oz. of the fused borax 
in an enamelled saucepan with water, boil 
rapidly for five minutes, decant, add fresh water, 
and repeat until all the borax is dissolved. For 
use, take three parts of the saturated solution 
(cold) and add one part of water. For trans- 
ferring, fill a large basin or dish with the borax 
solution. The plate, after its final washing, is 
stood in a rack for a few minutes to drain off 
the surplus moisture. The penknife is then very 
carefully passed along the fourth edge of the 
film, which must not be cut through by drawing 
the blade along, as that would pucker or tear 
the film. The plate is now placed in the basin, 
and the film will float off the glass, which can 
then be withdrawn. With a camel-hair brush 
turn over the film in the solution so that the 
collodion side is downward; if the fingers were 
used there would be a risk of damaging the loose 
film or of abrading the powdered side. The 
plaque or other support is next introduced under 
the floating film, which is guided into its correct 
final position. The support is then slowly, and 
by degrees, lifted out of the water with the film 
adhering, powder side uppermost, and placed 
on blotting-paper to dry, after which loose pieces 
of film may be removed with a damp sponge, 
and the image should be very carefully examined 
for any black spots or imperfections, the former 
being removed with a fine needle-point set in 
a wooden handle. The delicate powder is next 
protected by flowing over it— 

.. Fatty oil of turpen- 

tine 


: ' IO mins. 
Oil of turpentine 


I OZ, 


20 CCS. 


I,000 ,, 


Oil of turpentine oxidises by exposing for some 
time to light and air. The mixture should be 
filtered and kept from the dust. When dry, the 
plaque coated with this medium should appear 
uniformly dull. Any white spots on the picture 
may now be filled in with a little of the powder 
colour mixed with the medium above mentioned. 
If the plaque is given a light firing, just sufficient 
to attach the powder to the surface, it can be 
spotted or worked upon with facility. 

Firing is the next process. The work will be 
fired at any pottery for a moderate charge; 


98 


Ceramic Process 


but by the aid of a gas muffle the worker can 
easily do his own. For tiles and plaques the 
heat must be applied very carefully, gradually 
increasing the consumption of gas. When the 
furnace is fully heated the gas is immediately 
turned out, the chimney covered up, and the 
whole left to cool, or, instead, the work can be 
transferred to an annealing chamber. Enamel 
plaques or medallions on a metal base need not 
be cooled with such extreme care. 

Dust is especially to be avoided in ceramic 
work; it is advisable to sprinkle the floor of the 
room with water, which will probably suffice to 
lay the floating dust, and on no account should 
any sweeping or dusting be done immediately 
preceding any of the manipulations. Charging 
the air with moisture by means of a spray 
diffuser or vaporiser prevents the dust nuisance, 
but makes the room too moist for developing. 

It may be said that the image may be printed 
direct on perfectly flat surfaces, instead of using 
a temporary support. 

There are many possible modifications of the 
above process. (1) Instead of using the dusting- 
on process, a film prepared with ferric chloride 
may be employed. ‘The film is exposed under a 
negative to obtain a plate of various degrees of 
tackiness, which is then brushed over with 
powdered enamel colour as before. No trans- 
parency is required. The picture so obtained is 
coated with collodion, stripped, and treated as 
before described. (2) Prints obtained by the 
carbon process, simply substituting enamel 
colours in the preparation of the film, may be 
developed upon porcelain as a final support, 
forming excellent pictures for firing. (3) A 
method that is useful where numbers are re- 
quired is to obtain a photo-mechanical impres- 
sion in the usual manner on a special transfer 
paper prepared with a collodion substratum. 
A suitably tacky ink is used for printing, and 
the ceramic powder is dusted over this. The 
paper is then moistened and removed, while 
the film and picture, collodion side downwards, 
are transferred to the porcelain support or 
plaque, which is first treated with an adhesive 
medium. (4) The following procedure may be 
taken as representative of the substitution pro- 
cess. A collodion positive is obtained in the 
camera by the wet process, fixed, washed, 
bleached in a 5 per cent. solution of mercuric 
chloride, again washed and placed in the sub- 
stitution bath, which is to replace the original 
image, unsuitable for firing, with one of platinum 
or iridium. A gold and platinum bath, as 
follows, gives a purple-brown colour :— 


Potassium chloro- 


platinite : - 8 -grs. 1s” &: 
Gold chloride (1in60) 44 drms. 43 ccs. 
Water (distilled) 44 Oz. 345 55 
Lactic acid . - 5 mins. > |, 


An iridium and gold bath gives a warm black 
tone :— 


Iridium chloride 8 grs. Is @€. 
Gold chloride (1 in 60) 44 drms. 43 ccs. 
Water (distilled) 44 oz. S46 5; 
Lactic acid 6 mins. I 


”» 


After the deepest shadows of the picture have 
been toned through, wash for a few minutes to 


po 


Cerate Paste 


femove the free toning solution. Cut round 
the margins of the film, immerse the plate in a 
I per cent. solution of sulphuric acid, wash the 
film after it strips off, transfer to the final sup- 
port of porcelain, collodion side up, and dry. 
Then remove the collodion film by gently rub- 
bing with a sponge moistened with ether and 
alcohol, again dry, and dust the image with 
flux, when it is ready for firing. (5) Itis possible 
to obtain a burnt-in picture in natural colours 
by the exact superposition of a blue, a red, and 
a yellow picture printed from three negatives 
obtained through suitable screens. The yellow 
film is first transferred and fired, allowed to cool, 
and the blue image very carefully superposed 
on this in exact register and burnt in. After 
again cooling, the red film is transferred and fired. 


CERATE PASTE 

A paste or waxy mixture for surface applica- 
tion to finished prints. Better known as 
encaustic paste, under which heading formule 
will be found. 


CERIC SULPHATE (Fr., Sulfate de cérium, 
Sulfate cévique ; Ger., Cerisulfat) 

Synonym, sulphate of cerium. Solubilities, 
slightly soluble in water, more soluble in dilute 
sulphuric acid. Ce(SQ,), 4H,O. Molecular 
weight, 404. It occurs as reddish yellow crystals, 
and was suggested by Lumiére as a reducer, the 
formula being :— 


Ceric sulphate rn OZ. 100 g. 
Sulphuric acid . 384 mins. 40 ccs, 
Distilled water to . 20072. TOO. a 


This acts very energetically, and can be diluted 
for prints and lantern slides. A 5 per cent. 
solution acts more strongly on the high lights of 
a negative than the shadows. 


CERIO PRINTING . 
A term commercially applied to the kallitype 
process (which see). 


CERIUM SALTS, PRINTING WITH 

There are two series of cerium salts, a cerous 
and a ceric, the former being stable, but the 
latter extremely unstable; this fact induced 
Lumiére and Seyewetz to examine their photo- 
graphic properties, and they found that ceric 
sulphate and nitrate, when used for sensitising 
gelatinised paper with exposure under a positive, 
were reduced to the cerous state, and became 
pale coloured. The print, being then treated 
with certain organic substances, gave coloured 
images, due to the formation of dyes through 
the oxidation of the developers by the unre- 
duced ceric salts, and the dye images thus formed 
wete insoluble in water. In an acid solution 
phenol gives grey images; aniline salts give 
greens; naphthylamine gives blue; amido- 
benzoic acid, brown; parasulphanilic acid, 
ted; and ortho-toluidine salts, brown images. 
With ammoniacal solutions other colours are 
obtained ; for instance, aniline gives violet and 
naphthylamine reddish violet images. Paper 
sensitised with these cerium salts is far more 
sensitive than with iron or manganese salts and 
the range of colours is far greater, but no com- 
mercial application of this process has yet been 
made, 


Chalk 


CEROGRAPHY 


The art and process of engraving on wax. 
(See ““ Wax Engraving.’’) 


CEROLINE (Fr., Cévoline; Ger., Ceroline) 


A solution of white wax in benzole, used in 
the early days to render paper translucent. 


CERTINAL 


A highly concentrated liquid developer in one- 
solution form, introduced by Ilford Ltd., March, 
1909. The best proportion for developing plates 
and films which have received normal exposure 
is certinal 24 drops, water 1 oz. At a tempera- 
ture of 60° F. (nearly 16° C.) the image appears 
in a few seconds, and development will be com- 
plete in from 4 to 8 minutes, according to the 
plate and the class of negative desired. The 
rapid appearance on dry plates must not be mis- 
taken for signs of over-exposure, and the image 
will need to be developed for density. Asa rule, 
the image on a properly exposed plate appears 
in 15 seconds, and development is complete in 
6 minutes. With under-exposure the best 
results are obtained by using the developer 
weaker (16 drops of certinal to each ounce of 
water) and developing longer. Over-exposed 
plates need a stronger developer and the addition 
of potassium bromide (certinal 48 drops, water 
I 0z., 10 per cent. solution of bromide 48 drops) ; 
development will then take about one-fourth less 
time than would be required when exposure and 
developer are normal. For tank or stand 
development } oz. (120 drops) of certinal should 
be added to 25 oz. of water; development will 
be complete in from 30 to 60 minutes, according 
to temperature, plate, subject, and type of 
negative desired. For lantern plates and 
bromide paper the best strength is 16 drops to 
each ounce of water, but gaslight papers and 
plates need double that strength. More con- 
trast may be obtained on papers and lantern 
plates by using a stronger developer, and still 
more by adding potassium bromide, while softer 
results are obtained by diluting the developer. 
Additional bromide gives warmer blacks, especi- 
ally on gaslight papers and plates, 


CHALK (Fr., Crate; Ger., Kreide) 

Precipitated chalk, a fine white substance, is 
a pure form of carbonate of lime. It is often 
used for neutralising gold toning baths, for which 
purpose common whiting (prepared from chalk 
by grinding and levigating) is sometimes used ; 
chalk is also used for clearing varnishes. 

In process work, precipitated chalk or washed 
whiting is largely used for cleaning glass, for 
giving a final polish to copper and zinc plates, 
so as to remove grease (the chalk being made 
into a paste with ammonia), and for rubbing in 
an engraved plate, so that the image may show 
up and enable the engraver or fine etcher to 
do any retouching that may be required. Mag- 
nesia is, however, more generally used now for 
the latter purpose, the chalk often tending to 
grittiness. 

Lithographic chalk is somewhat a misnomer, 
this substance being the black, greasy, crayon 
used for drawing on grained lithographic stone, 
zinc, or aluminium, and for drawing on grained 
transfer papers. The term no doubt originated 


Chalk, French 


from the similarity of the crayons to ordinary 
black and white chalks used for drawing on 
paper. 

Chalk ink is a stiff black lithographic ink used 
for inking-up lithographic drawings in chalk on 
grained surfaces. 

Chalk transfer paper is a grained paper for 
drawing upon with lithographic chalks. 


CHALK, FRENCH (Fr., Talc, Savon a marquer ; 
Ger., Talk, Franzésische Kretde) 

Synonyms, talc and steatite. French chalk is 
a hydrous silicate of magnesia, a typical analysis 
being: silica 62, magnesia 33:1, and water 
4°9 per cent.; 1 or 2 per cent. of iron often 
occurs as well. It has the appearance of a fine 
white or greyish white powder, and is used 
chiefly for polishing glass, to which prints are 
squeegeed for the purpose of glazing. 

In process work, it is used for polishing glass 
for stripping purposes, and also as a resist for 
etching, for which latter purpose it is dusted 
upon an ink.image. It is especially useful in 
this way in lithographic work on stone, and it is 
sometimes employed in admixture with black- 
lead. 


CHALK PLATE 


An iron plate thickly coated with a chalky 
substance, through which a drawing is scratched 
with a pointed stylus. The plate is then used 
as a matrix for stereotyping. 


CHALKINESS (NEGATIVES AND 
PRINTS) 

‘* Hardness’’ or excessive contrast; chalky 
negatives and prints show a very great differ- 
ence between the high lights and deep shadows. 
The fault is due to under-exposure and over- 
development, and a partial remedy is the ammo- 
nium persulphate reducer. Softer prints may 
be obtained from such negatives by bleaching 
with, say, a mercuric bichloride solution as 
used for intensifying, and printing from the 
negative in its bleached or whitened condition. 
There is no complete remedy for chalky or 
hard prints. 


CHALKINESS (WATER) 


Water, particularly hard water, is some- 
times chalky, and although it rarely does any 
harm to solutions it is better to boil it before 
use (see ‘‘ Water’’). Dr. Hauberisser has 
described a chalkiness which comes over the 
negative in a kind of fog, and is due to impurities 
in the water, these giving rise to an insoluble 
calcium compound. When water containing not 
enly sodium chloride, but a calcium salt as well, 
is used, there is the risk of calcium oxalate being 
formed should a ferrous oxalate developer be 
employed. Similarly, with water containing 
organic agents, the use of potassium carbonate 
may cause calcium carbonate to be precipitated 
as a sediment in the gelatine, thus producing a 
calcic fog. A simple remedy for such a deposit 
consists in the application of a weak solution of 
hydrochloric acid to the negative, this convert- 
ing the calcium carbonate to soluble calcium 
chloride, which, of course, washes out. There 
may, however, be a risk of the liberated carbon 
dioxide causing blisters. 


100 


Charcoal, Wood 


CHANGING BAGS AND BOXES 


A changing bag isa device to allow of reloade 
ing dark-slides or sheaths without the necessity 
fora dark-room. It is generally a bag of several 
thicknesses of black and red material, provided 
with sleeves which tighten round the arms by 
means of elastic, so that the hands are inside 
the bag. In some forms the changing has to 
be effected by the sense of touch alone; in others 
there is an eye-piece to fit on the face so that 
the interior of the bag can be seen, light being 
admitted through a panel of red fabric or cellu- 
loid in one side of the bag. The utility of such 
a bag as a makeshift dark-room is obvious. 

A changing box is a magazine holding plates 
in sheaths, and is generally detachable from the 
camera. An exposed plate can be moved from 
the front to the back, or an unexposed plate 
taken from the back and placed in front of the 
one last exposed. The usual method of accom- 
plishing this is to raise the plate into a bag of 
flexible leather and place it in position by hand, 
but in some cases the transfer is made mechanic- 
ally. The front of the changing box is fitted 
with a draw shutter, which is opened for expo- 
sure and closed when the box is to be removed 
from the camera. The back of the box can be 
opened for the removal of exposed plates and 
for reloading the sheaths. Hence there is some 
advantage in those types in which the exposed 
plates find their way to the back of the box, 
as they may be removed without disturbing 
unused plates. Many boxes are constructed to 
take cut films instead of plates, their capacity 
thus being doubled. Obviously the number of 
plates or films available may be increased by 
the use of additional changing boxes. (See also 
“Daylight Changing.’’) 


CHARBON VELOURS (Fr.) 


The name originally given to the paper intro- 
duced by V. Artigue, of Bordeaux, in’ 1892 
(see “‘Artigue Process’), A recipe for making 
a similar paper is given under the above 
denomination by H. Schneeberger. The pig- 
ment may be any ordinary water-colour; or 
moist colours may be used, provided they do not 
contain a tanning ingredient. The colour is 
rubbed up in a stiff paste of starch and applied 
to the paper in a thin uniform coating. Too thin 
a coating, or one containing insufficient pigment, 
does not give the desired velvety appearance ; 
while, if too thick, the half-tones and other parts 
where the light has not penetrated to the support 
are apt to wash away in developing. The coated 
paper will keep indefinitely. It is sensitised, for 
flat negatives, in a 2 per cent. bath of potassium 
bichromate, or, for hard negatives, in a 5 per 
cent. bath. Development is with a warm saw- 
dust mixture, asin the Artigue process, a temper- 
ature of about 80° F. (about 27° C.) being recom- 
mended. 


CHARCOAL, ANIMAL 
Known generally as bone black (which see). 
CHARCOAL, WOOD (Fr., Charbon de bois ; 
Ger., Holzkohle) 


Wood charcoal is the residue from the destruc- 
tive distillation of wood. Wood having been 
heated to a high temperature out of contact with 


Chardon's Process 


the air, the volatile portions are driven off, and 
the yield is very nearly pure carbon, Sticks of 
charcoal made from vine or willow wood are 
used as crayons for working up enlargements. 

In process work, blocks of charcoal are used 
for polishing the metal plates. Formerly, 
selected sticks of willow charcoal were used, but 
of late years this has been superseded by char- 
coal made of trimmed blocks of soft pine. 
Such charcoal comes from the United States, 
and is known as ‘“‘ American charcoal.” It is 
beautifully soft and even in texture, and can 
be had in “hard” and “soft” qualities, 


CHARDON’S PROCESS (Fr., Procédé Char- 
don; Ger., Chardon’s Prozess) 

A collodion emulsion process due to Alfred 

Chardon, who won with it the prize of 1,000 

francs offered jointly, in 1876, by the Photo- 


gtaphic Society of France and A. Liebert, of- 


Paris, for the best and most reliable dry process 
for outdoor use. It was, as its author stated, 
more a well-judged selection and combination of 
the best points of other processes than an original 
or new method, although possessing some novel 
features: as the use of two different kinds of pre- 
cipitated pyroxyline; washing the emulsion by 
pouring it into the water, instead of the reverse, 
as was formerly done; the employment of 
glucose in the developer to obtain density, etc. 


CHEMICAL FOCUS (Fr., Foyer chimique ; 
Ger., Chemischer Brennpunkt) 

The plane on which the actinic rays are brought 
to a focus. In simple periscopic or non-achro- 
matic lenses, the focal plane for the actinic rays 
lies nearer the lens than that of the visual rays; 
it follows, therefore, that the sharp image 
obtained by focusing, which is affected by the 
visual rays, is not reproduced by the sensitive 
film on which the actinic rays act most. This 
defect, which is rarely met with now, can be 
remedied either by reducing the distance between 
the lens and plate, after focusing and before ex- 
posure, by from 54 to ; of the extension of the 
camera, or by the temporary insertion, only 
whilst focusing, of a weak supplementary lens 
which reduces the focal length. 


CHEMICAL FOG (See “ Fog.’’) 
CHEMICAL RAYS (See “ Actinic.’’) 


CHEMICAL RETOUCHING (See “ Re- 
touching, Chemical.’’) 


CHEMICALS 

A list of the chemicals used in photography, 
with their formule and solubilities, appears under 
the heading “‘ Solubilities.”’ 


CHEMICALS, STORING 

Chemicals need careful storing if they are to 
be kept good and in a proper working condition. 
Those given below are the chemicals mostly 
used in photography, and the remarks apply 
generally to the chemicals themselves, as bought, 
and not to made-up solutions, as developers, 
intensifiers, etc., for information as to which 
see under the heading ‘‘Solutions.’’ Photo- 
graphic chemicals may be divided into four 
classes—namely :— 


IOI 


Chemiglyphy 


(1) Chemicals that keep well and need no 
Special precautions, other than being stored in 
a dry place :— 


Alum (ordinary and Potassium bichromate 
chrome) Potassium bromide 
Borax Potassium ferricyanide 
Boric acid Potassium oxalate 
Caramel Sodium acetate 


Citric acid Sodium carbonate 
Mercuric chloride Sodium hyposulphite 


(2) Chemicals that must be kept in bottles 
with tight-fitting corks (not glass stoppers) 
because of their deliquescent nature or oxidising 
properties :— 

Adurol 

Amidol 

Ammonium carbonat 

Ammonium sulpho- 
cyanide 

Fikonogen 

Ferric chloride 

Ferrous sulphate 


Magnesium powder 
Potassium carbonate 
Potassium cyanide 
Potassium hydrate 
Potassium iodide 
Potassium metabisul- 
phite 
Pyrogallic acid 


Formosulphite Sodium hydrate 
Glycin Sodium sulphate 
Hydroquinone Sodium sulphite 
Metol Uranium nitrate 


and all other dry developers not mentioned 
above, as metoquinone, pyro-catechin, etc. 

(3) Corrosive and volatile substances, which 
should be kept in bottles having accurately 
ground glass stoppers, not corks :— 


Acetic acid Collodion 
Acetone Ether 

Alcohol Formaline 
Ammonia (liquor) Hydrochloric acid 
Ammonium  persul- Todine 


phate Nitric acid 
Amyl acetate Sulphuric acid 


(4) Materials that should be kept in a dark 
cupboard, or in black bottles when not in use :— 


All kinds of liquid aniline dyes. 
Gold chloride in solution. 

Potassium chloroplatinite in solution 
Silver nitrate, dry and in solution. 


Chemicals that are poisonous, or otherwise 
dangerous, should be stored in a cupboard or 
some out-of-the-way place where they cannot 
be got at by persons unacquainted with their dan- 
gerous properties. Such chemicals include :— 


Acetic acid Sodium oxalate 
Hydrofluoric acid Chromic acid 
Nitric acid Hydrochloric acid 
Chrome alum Sulphuric acid 


Ammonium bichro- Ammonia 

mate Ammonium oxalate 
All soluble barium Bromine 

salts Formaline 


Lead acetate 
Potassium oxalate 
Caustic soda 


Soluble copper salts 
Lead nitrate 
Potassium bichromate 
Caustic potash Sodium bichromate 
Silver nitrate All developers 


These are in addition to the scheduled poisons, 
all of which must be kept in a safe place. 


CHEMIGLYPHY 
Another name for “‘ Glyphography ” (which see). 


Chemigraphy 


CHEMIGRAPHY 


A general name, not often used now, for zine 
etching. (See also ‘‘ Chemitype.’’) 


CHEMITYPE 
Before the application of photography to zinc 
etching, lithographic transfers or drawings direct 
on zinc were etched into relief for letterpress 
rinting. This process was generally called 
‘“* Chemitype ”’ or “ Chemigraphy.” 


CHIAROSCURO (It.) 


A word adapted from the Italian chiaro, clear, 
and oscuro, dark, and indicating the light and 
shade in a picture. The suitable placing of the 
highest light and the deepest shadow is of great 
importance. Scattered high lights and disjointed 
shadow masses afe fatal to harmonious effect. 
The portraits of Rembrandt are good and familiar 
examples of effective knowledge of the value of 
proper chiaroscuro. 

Chiaroscuro is the name of a class of colour 
prints in which the varying effects of light and 
shade are represented, not by lines or cross- 
hatching, as in ofdinary engraving on wood or 
metal, but by tones in the shape of broad masses 
of colour, produced by surface printing from 
wood-blocks. These were usually employed for 
the purpose of colouring an outline woodcut. 


CHILDREN, PHOTOGRAPHY OF 

The success or failure in photographing a 
child is nearly always dependent on the ability 
of the operator to gain the confidence of his 
juvenile sitter. In the case of amateur work, 
the child is often personally acquainted with the 
photographer, but in professional work the child 
is probably a complete stranger to the operator. 
It is useless to treat a child in the same manner 
as an adult, and simply request it to assume 
the desired position. Particular art is necessary 
in getting the child to adopt the pose required. 
Too many friends of the child should not be 
allowed into the studio, one being quite enough ; 
otherwise difficulties are likely to ensue, especi- 
ally in the case of very young children whose 
attention is very easily diverted. Children 
differ so much in their disposition that it is 
possible to make friends easily with some, 
whilst others are shy and require quite diplo- 
matic handling. In some cases it is better to 
ignore the child at first, and to engage in con- 
versation with whoever is in attendance on the 
child, and then, by opening a picture-book, 
operating a mechanical toy, introducing a dog 
or cat, the child becomes interested and gradu- 
ally its confidence is won. Some of the most 
successful child photographers have cultivated 
an ability to bring themselves down to the 
children by playing games and in other ways 
giving them the impression ‘“‘ that they are one 
of themselves.”’ By this means they engage a 
child’s attention, until both the desired position 
in the studio and the happy expression are 
attained, at which juncture an assistant makes 
the exposure. 

The introduction of modern high-speed plates 
has given new possibilities to child photography. 
Some few years ago it was necessary to draw up 
all the studio blinds so as to admit as much light 
as possible, but although this allowed a quicker 


102 China, Photographs on 


exposure to be made, the picture was devoid of 
all light and shade gradations. The plates at 
present available allow of a more subdued light 
being used; and proper attention should be 
given to the arrangement of blinds for con- 
trolling the lighting. 

The studio reflex camera is at present but 
very little used, but for child photography it 
possesses very great advantages, as it frequently 
happens that when the child has been correctly 
focused and the dark-slide inserted for exposure, 
the child moves to some other position, necessi- 
tating re-focusing. With a reflex camera this 
trouble is avoided, as it is possible to focus the 
sitter right up to the moment of exposure. 

The dress of the child often makes or mars 
a picture, and some photographs owe their 
charm almost entirely to dainty garments. On 


_the other hand, quite young children usually 


make more pleasing pictures when photographed 
either nude or with only a single garment on. 
Amateur work takes place under varied con- 
ditions, some workers possessing lofty rooms 
with abundant light in which it is possible to 
obtain pictures equal to those produced in a 
studio; but for those not so fortunate special 
arrangements must be made so as to obtain 
sufficient light for the quick exposures necessi- 
tated. In an ordinary room with a bow window 
it is often an advantage to take away all existing 
blinds and hangings, as these, when drawn up 
or to the side, frequently cut off much light. 
The window-panes may be covered with tissue 
paper, as this gives a more equal diffusion of 
light; on the shadow side a screen should be 
used with a sheet thrown over it for use as a 


reflector, but care must be exercised not to move © 


this reflector too close to the child, otherwise 


too flat a lighting is obtained, and there is great . 


tisk of producing false lights in the eyes. As 
children are usually taken so as to show the 
entire figure, it is necessary to see that the light- 
ing reaches well down to the ground; to accom- 
plish this it is sometimes useful to build up a 
platform some 12 in. or 18 in. from the floor. 
Care must be taken to prevent the light coming 
too much from the side, and so to arrange the 
light that the strongest portion of it falls from 
a point higher than the child’s head. This can 
be attained by covering the lower panes of the 
glass with three or four thicknesses of tissue 
paper. In photographing children out of doors, 
good lighting is possible if care is taken to choose 
a position where the light is screened from one 
side; this is easily done by utilising the side of 
a house and arranging the sitter near to it, so 
that the main direction of light falls from the 
side and front. If a head screen is available it 
should be used to cut off the immediate top 
light. An entrance doorway or portico is very 
often suitable for such portrait work. (See also 
““Home Portraiture,” “‘ Studio Portraiture,” etc.) 


CHINA CLAY (See “ Kaolin.’’) 


CHINA, PHOTOGRAPHS ON 

There ate several methods of printing photo- 
gtaphs upon china, crockery, opal, etc. For 
objects where the picture is to be viewed by 
reflected and not transmitted light, the carbon 
process (which see) is perhaps the best; tissue of 


China, Photographs on 


any colour may of course be used, and the pic- 
ture, after being printed upon the tissue, is 
transferred and developed upon the china sup- 
port, after the latter has been properly prepared 
with a suitable substratum. By this process it 
is an easy matter to transfer photographs upon 
curved surfaces. The ceramic process (which 
see) is more difficult, but the results are abso- 
lutely permanent and will permit of any amount 
of washing. 

The blue-print (ferroprussiate) process is 
simple, and is often employed for producing 
pictures upon china and glass. It will be neces- 
sary to give the article a coating of gelatine to 
serve as a vehicle for holding the sensitive solu- 
tions, the blue-print being a direct printing and 
not a transferring process, as carbon. A suit- 
able gelatine substratum may be made by 
soaking 22 gts. of Nelson’s No. 1 gelatine in 
1 oz of water and melting by the aid of heat, 
afterwards filtering while hot. The solution, 
when warm (130° F. or 54° C.), is coated as evenly 
as possible upon the part of the article to be 
printed upon, and then set aside to cool. The 
prepared part is then sensitised as if it were 
paper, and when dry it is ready for printing upon. 


—— 


Printing on Vase 


Collodion has also been recommended as a 
vehicle for the blue sensitising solution, and the 
tesults are perhaps more permanent. The 
formula is: pyroxyline (high temperature) 
120 gts., methylated alcohol (-820) 6 oz., and 
methylated ether 5 0z. Mix a day or two before 
using, allow to settle, coat the article with the 
mixture, and when set sensitise with the “ blue- 
print”? mixture. Substratums of collodion have 
been known to peel off, and to prevent this the 
places where the edge of the collodion is to come 
should be treated before coating with a solution 
of indiarubber in benzole. 

Ordinary glass negatives can only be employed 
for printing when the surface is flat; on curved 
sutfaces film negatives may be kept in contact 
by means of elastic bands, as shown in the illus- 
tration, or by means of gummed paper at the 
corners. As it is not desirable to remove the 
negative from the vase for the purpose of exam- 
ing the progress of printing, there must be 
something left to chance, or an actinometer 
must be used. It is advisable to varnish such 
pictures when dry. Blue pictures may be toned 
to a different colour by any of the methods 
advocated under the heading “ Blue-print Pro- 

cess,” sub-heading “ Toning Blue-prints.” 


103 Chloral Hydrate 


CHINA, PHOTOGRAPHY OF 

The principal difficulties in photographing 
china arise from the highly glazed surface and 
the consequent reflections. These may be 
minimised, if not altogether destroyed, by 
attention to two points. The lighting should 
never be from the front, but well towards one 
side—almost a side lighting. An inspection of 
the pieces being photographed from the position 
of the lens will show when the lighting produces 
no direct reflections. Im addition, a plain, 
dark-coloured cloth should be hung immediately 
behind the camera, so that no light or bright 
objects may produce reflections. A colour- 
sensitive plate and a yellow screen should also 
be employed. In addition to giving a better 
and a truer rendering of the ornamentation, 
this also assists in reducing the effects of 
reflections. 


CHINA SILK 


A soft material, recommended for cleaning 
lenses, prisms, screens, and other optically- 
worked glass surfaces. In using china silk for 
cleaning ruled screens, merely breathe on the 
surface before rubbing. 


CHINESE WHITE 

This white water-colour pigment, which con- 
sists of zinc oxide, though formerly much used 
for retouching photographs for reproduction, 
has been largely superseded by Albanine, Blanc 
d’Argent, and Ulimanine. The objection to 
Chinese white is that it photographs darker than 
paper; it may, however, be used for mixing 
with other pigments to form a body colour. 
R. W. Wood has shown that Chinese white 
photographs black in ultra-violet light. 


CHINOLINE BLUE (See “ Cyanine.’’) 


CHINOLINE RED (Fr., 
Ger., Isochinolinerot) 
Synonym, isochinoline red. A complex, 
organic dye, obtained by heating benzole 
trichloride with chinaldine and isochinoline. It 
is extremely sensitive to light, and this induced 
Vogel to test it as a sensitiser (see ‘“‘ Azaline’’). 
It has now been almost entirely replaced by the 
isocyanines, but Dr. Miethe has stated that a 
small addition to an isocyanine bath keeps the 
plates free from fog; and the following is a 
typical formula :— 


Quinoléine rouge ; 


Isocyanine dye sol. (1:1,000 


water+alcohol) . ! . 10 parts 
Chinoline red (1:1,000 w.+alc.) 50 ,, 
Water to ° : : * 300.) 


The chinoline red also helps to fill up the usual 
gap in the green. 


CHLORAL HYDRATE (Fr., Chloval hydrate ; 
Ger., Chloral hydrat) 

Synonym, trichloraldehyde. CClI,CH(OH).. 
Molecular weight, 165-5. Solubilities, very solu- 
ble in water, alcohol, and ether. It is poisonous, 
the antidotes being ether, cocaine, and camphor. 
It occurs as transparent, colourless crystals or 
flat crystalline masses, obtained by the action 
of chlorine on aldehyde, with peculiar pungent 
odour and taste. It has been recommended as 


Chlorates 


a solvent of gelatine for making a mountant, 
and has been suggested for making a non- 
inflammable film. 


CHLORATES (Ftr., Chlorates ; 
saures) 
Salts formed by the action of chloric acid, 
HC10;, such as potassium chlorate, KCIO,. 


CHLORHYDRIC ACID 
Acid.’”’) 


CHLORIDE OF LIME TONING BATH 

A toning bath, suitable for albumenised paper. 
Fifteen grains of chloride of gold should be dis- 
solved in 1 oz. of water, a few grains of prepared 
chalk added, the solution well shaken, allowed to 
settle, and then filtered, the clear solution being 
used for making up the bath. The formula is :— 


Sodium acetate 


Ger., Chlor- 


(See “‘ Hydrochloric 


SO CUts. soe. 

Chloride of lime . : 1} ,, aPLang 
Gold chloride (1 oz. of 

solution as described) . 15 mins. 1°2 ccs. 

Water . g : 30 202, 1,000 7% 


This forms a stock solution which improves by 
keeping. For use, take 2 oz. and add 8 oz. or 
10 oz, of water, this being sufficient for eight 
whole-plate prints. 


CHLORIDE PLATES AND PAPERS 

Plates or paper coated with a slow gelatino- 
chloride emulsion intended for development. 
(See “‘ Emulsion.’’) 


CHLORIDES (Fr., Chlorures ; Ger., Chloride) 

A salt formed by the action of hydrochloric 
acid, HCl, on metal, such as sodium chloride, 
NaCl. (See respective names of metals.) 


CHLORINATED LIME OR CHLORINATE 
OF LIME (See “Lime.”) 


CHLORINE (Fr., Chlore ; Ger., Chior) 

Cl. Atomic weight, 35:5. A yellowish green, 
gaseous element, obtained commercially by 
heating manganese dioxide with hydrochloric 
acid. A solution of chlorine has been employed 
as a “hypo” eliminator. 


CHLOROBROMIDE EMULSION 
An emulsion containing both chloride and 


bromide of silver, the former being in excess. 
(See “ Emulsion.’’) 


CHLOROCYANINE 


Eder stated that ordinary (iodo-) cyanine acted 
better as a sensitiser and that it gave plates 
freer from fog if it was treated with hydro- 
chloric acid; but K6nig has pointed out that 
this process only purifies the cyanine, and does 
not form chlorocyanine. 


CHLOROFORM (Fr. Chloroforme ; Ger., Chloro- 
form) 

Synonyms, trichloromethane, (improperly) 
forniyl trichloride. CHCl. Molecular weight, 
119°5. Solubilities, 1 in 200 water, miscible with 
alcohol, ether, and benzole. It is poisonous, the 
antidotes being emetics, the use of the stomach 
pump, fresh air, cold douche, strychnine hypo- 


104 


Chromatic Aberration 


dermically. It must be kept in the dark. It 
is a heavy, colourless liquid, with characteristic 
sweet smell and taste, and is obtained by the 
action of bleaching powder on alcohol or acetone. 
As a solvent of amber, etc., and indiarubber, it 
is useful for varnishes, 


CHLORO-IODO-BROMIDE EMULSION 


An emulsion containing chloride, bromide, 
and iodide of silver. 


CHLOROPHYLL (Fr., 
Chlorophyll) 
Solubilities, slightly soluble in water, soluble 
in alcohol and ether. The green colouring matter 
from plants, which was used as a red sensitiser 
for gelatine plates. 


CHLOROPLATINITE OF POTASSIUM 
(See “* Potassium Chloroplatinite.’’) 


CHLOROPLATINOUS ACID 
num Perchloride.’’) 


CHONDRIN (Fr., Chondrine; Ger., Chondrin) 
One of the constituents of gelatine (which see). 


CHOREUTOSCOPE 


A fitting for the optical lantern, designed by 
Beale, of Greenwich, to illustrate persistence of 
vision. It consisted of a eircular glass plate 
with images drawn upon it, which rotated in the 
lantern, zoétrope fashion. In a later and more 
simple form the images were drawn on a strip of 
glass, which was used in a special carrier. 


CHRIPOTYPE 


One of the many printing processes invented 
by Sir John Herschel, who named it “ Chryso- 
type”’ (which see). 


CHROMATED GELATINE 
chromated Gelatine.’’) 


CHROMATES 


sauresalz) 


Salts formed by the action of chromic acid, 
H,CrO,, on a metal, and having the formula 
M’CrO,. These salts are most of them highly 
coloured and sensitive to light in the presence 
of organic matter, 


CHROMATIC ABERRATION 
vation chromatique,; Ger., 
Abweichung) 


To arrive at a proper understanding of the 
cause of chromatic aberration, it is necessary to 
remember that a lens is practically a prism with 
the power of refracting or altering the direction 
of rays of light and, in an uncorrected form, of 
refracting rays of different colours to a different 
extent. Diagram A indicates the effect of 
passing a ray of white light through a prism; 
the bending of the rays will be noticed. The 
most active in their chemical action are the blue 
and violet, and these are diverted from their 
original path more than on the others; B shows 
two prisms placed base to base so that in the 
case of each colour. the rays are directed to a 
common point. The effect of this arrangement 
more nearly approximates to that of a simple 


Chlorophyile; Ger., 


(See “‘ Plati- 


(See “Bi- 


(Fr., Chromates ; Ger., Chrom- 


(Fr., Aber- 
Chromatische 


Chromatic Aberration 


lens as in C, where only three colours are in- 
cluded for the sake of simplicity. Such a lens 
is in fact a circular prism with the power of 
bending the rays of one colour so that after 
passing through it they meet at one point. This 
point is called the focus, and it will be seen that 
the focus for the blue-violet rays to which 
ordinary photographic plates are most sensitive 
is much nearer to the lens than the luminous 
rays, green-yellow, which are those that form 
the visual image upon the focusing screen. 
This is chromatic aberration in its simplest form. 
If the image produced by such a lens upon the 


Red 
Orange 


Yellow 


OTA 
rt Green 
Blue 


LN Violet 


A. Ray of White Light Passed through Prism 


ground-glass screen be examined with a magnifier, 
it will be found that the outline of any bright 
object, such as that of a white china knob, is 
surrounded with a fringe of colour, either blue 
ororange. Ifa photographic plate be substituted 
for the focusing screen there will be obtained 
a blurred outline, the image being “out of 
focus.””’ On moving the plate nearer the lens by 
one-thirtieth to one-fortieth of the total distance 
between the lens and the visual focus, there will 
be obtained on a plate an image which is prac- 
tically sharp. When using ordinary spectacle 
lenses, a course that is possible where extreme 
definition is not required, the precaution above 
mentioned must be observed. 

The avoidance of chromatic aberration in a 
photographic lens is effected by the use of at 


B. Rays Passing through Prisms Placed Base 
to Base 


least two kinds of glass possessing different 
degrees of refraction (or bending power) and 
dispersion (or power of spreading out the various 
colours). These glasses, in the case of ordinary 
landscape and portrait lenses, were usually 
(1) crown glass, which, if made to suitable curves, 
could be caused to give any desired degree of 
refraction with the minimum of dispersion; and 
(2) flint glass, which had a higher degree of re- 
fraction, but relatively a much greater dispersion. 
The simplest form of single achromatic lens is com- 
posed of a double convex crown element and a 


105 Chromic Anhydride 


double concave flint one (see D). In ordinary 
photographic lenses the optician combines the 
most visually powerful region of the spectrum, 
namely the green and yellow near the D line, 
and the most chemically active, namely the blue 
and violet near G. It will be seen that the red 
rays are neglected, but in ordinary photography 
this is of little moment. In three-colour work, 
in which one of the images is made through a 
red screen, a higher degree of correction is 
necessary, and by the use of a third variety of 
glass it is possible to bring the red rays to a 
focus in the same plane as the green and blue, 


Violet 


Ped 
Green es 
/Veliow ,! 


’ 
4 
e 


C. Rays Passing through Lens or Circular Prism 


so that images taken through screens of these 
colours are identical in sharpness and size. A 
lens of this description is called apochromatic 
(which see). Recent advances in glass manu- 
facture have rendered the old terms “ crown” 
and “flint”? somewhat meaningless, as_ the 
dispersive elements are now frequently made 
of special forms of crown glass. 


CHROMATISM 

A lens that possesses the defect of chromatic 
aberration, described in the previous article, 
is said to suffer from chromatism. 
CHROMATYPE (See ‘ Chromotype.’’) 


CHROME ALUM (See “ Alum.’’) 


D. Simplest Form of Single 
Achromatic Lens 


CHROME PIGMENTS 

Under this term are classified lemon chrome, 
which is chromate and sulphate of lead; chrome 
green, a mixture of chrome yellow and prussian 
blue; chrome yellow, a normal lead chromate; 
and chrome orange and chrome red, which are 
basic lead chromates. They are occasionally 
used in colouring prints, but possess little photo- 
graphic interest. 


CHROMIC ACID (See “‘ Chromic Anhydride.”’) 


CHROMIC ANHYDRIDE (Fr., Acide chro- 
mique ; Ger., Chromsaure Anhydrid) 
Synonyms, chromic acid, chromium trioxide. 
CrO;. Molecular weight, 100.  Solubilities, 
1 in 0-6 water, decomposed by alcohol. It is 
poisonous, the antidote being emetics, then 


Chromium Intensifier 


milk, white of egg, and calcium saccharate. It 
must be kept dry. It violently explodes when 
it comes in contact with organic substances. It 
is in the form of deep, reddish brown acicular 
ctystals, and is obtained by the action of sul- 
phuric acid on potassium dichromate. It has 
been suggested for bleaching prints, but the 
potassium salt is more generally used. 

In process work, chromic acid is used as an 
addition to the fish-glue enamel solution. It 
increases sensitiveness and hardens the film, 
making it hold better on the metal. The acid 
should be pure, in fine, needle-like, purple 
crystals, not the red efflorescent variety used 
for electric batteries. Chromic acid is also used 
with sulphuric acid for “‘clearing”’ the fish- 
glue image before etching, by which means it 
removes any scum from between the half-tone 
dots. 


CHROMIUM INTENSIFIER 


For this intensifier two stock solutions should 
be prepared; each will keep indefinitely. 


A. Potassium bichromate. 402z. 55 g. 
Water ° ° « SO! 55 + t,0OD COs, 

B. Hydrochloric acid fe PO 55 g. 
Water to . ° « FG. 5, FF 00G acs: 


The working solution is prepared by taking 
1 part A, 1 part B, and 2 parts water. The 
mixed solution will not keep. The plate, 
after being well soaked in water, is immersed in 
this solution until thoroughly bleached, and is 
next well washed until the yellow colour of the 
bichromate quite disappears, exposed to day- 
ight for a few minutes, and then redeveloped. 
Any alkaline developer may be employed, but 
pyro is not so suitable as those that are used for 
making bromide prints. Both amidol and me- 
tol-hydroquinone are good. A moderate degree 
of intensification is secured, the printing value 
being multiplied by 13; but if this should be 
insufficient, the operation may be repeated, and 
increased intensity will be obtained each time. 
The result is quite permanent. 


CHROMIUM POTASSIUM SULPHATE 


Commonly called chrome alum (which see, 


under the heading “‘ Alum ’’). 


CHROMO-COLLOTYPE 


A process of collotype printing in colours. 
The term is also applied to a method of com- 
bining collotype with chromo-lithography for 
colour printing. 


CHROMO-CRYSTAL 


A type of coloured photograph similar to 
crystoleum and popular in the early days of 
albumen prints. The print was pasted face 
downwards on a piece of thick plate glass, 
coloured at the back, and backed up with another 
piece of thick glass, the coloured picture having 
the appearance of being embedded in crystal. 
The method is now employed, with or without 
the back glass, for producing ornamental paper- 
weights and other fancy articles. 


CHROMOGRAM 


The name given by Ives to the three consti- 
tuent pictures for his Kromskop. 


106 Chrono-photography 


CHROMO - PHOTOGRAPHS 


An early name given to photographs coloured 
from the back, now known as crystoleums (which 
see). 


CHROMOSCOPE 


The earlier name of the Ives Kromskop 
(which see). 


CHROMOTYPE 


A process of reproduction in colours by means 
of half-tone blocks, either by three-colour or 
four-colour printings. 


CHRONOMETRIC SHUTTER (Fr., Obtura- 
teur chronométrique ; Ger., Chronometrischer 
Verschluss) 

A shutter mechanically geared to give a pre- 
cisely timed exposure, or successive exposures 
at accurately recurring intervals. 


CHRONO-PHOTOGRAPHY 


The art of making photographic records of 
the motion of an object in chronological order. 

In the year 1870, Prof. E. J. Marey, of 
France, commenced his researches on the analysis 
of motion, and the advance in sensibility of 
photo-surfaces has lent continual aid from that 
time onward. The object of chrono-photo- 
graphy is to discover the successive attitudes 
which collectively make up a given motion, and 
to embrace phases of a swiftly-moving object 
otherwise escaping the notice of the unaided 
human eye. From a physiological point of 
view, this branch of the photographic art has 
proved of inestimable value, and it has served 
to dispel from the minds of artists certain 
erroneous ideas hitherto held regarding the 
various poses assumed by animals, birds, and 
the like, during the evolution of their movements. 

In the year 1865, Messrs. Onimus and Martin 
exposed the bared heart of a living animal before 
an open lens for the purpose of photographin 
it while in motion. With the low degree o 
sensibility then obtaining among photo-surfaces, 
the exposure necessarily extended over one or 
more pulsations of the heart, but as a pause 
takes place at each extreme of the heart’s beat 
the outline of these positions was better defined 
than the space between, and a record was there- 
fore obtained of the maximum and minimum 
limits of a pulsation. Clearly it is only necessary 
to secure outlines of several intermediate posi- 
tions in order that the experiment should attain 
this character of chrono-photography, properly 
so-called. A photograph of a man lifting his arm 
would (if the exposure lasted during the whole 
movement) result in a blur, but if a number of 
separate exposures was made in the same time 
a series of overlapping images, equal in number 
to the exposures, would occupy the place of one- 
exposure blur, and the outlines of these images 
would in addition form a perfect record of the 
successive positions of the arm. An ocular 
demonstration of these phenomena may be 
readily produced by means of any ordinary photo- 
graphic camera, supplemented with a disc per- 
forated with a number of holes, and so attached 
to the lens that by rotating the disc each of the 
apertures comes opposite the lens in succession. 
By pointing the apparatus to cover a man walking 


Chrono-photography 


along the footpath, and observing the inverted 
image on the ground-glass screen of the camera, 
meanwhile rotating the aperture disc, successive 
and clearly defined images of the man will be 
seen. Marey’s chrono-photographs were obtained 
somewhat in this way, and diagram A shows his 


A. Marey’s Device for Obtaining 
Chrono-photographs 


precise apparatus. A sensitive plate was placed 
in a slide at p. A disc with apertures revolved 
between the lens and the plate. On turning the 
handle at the side, which communicated the 
necessary motion to the disc, a rapid succession 
of images was secured. Marey found that the 
images, which were almost superposed, made it 
difficult to distinguish individual phases. To 
overcome this defect the subject, as shown at B, 
was attired in a black velvet suit, with dots and 
white lines marked thereon. During the act of 
photographing, the subject ran, jumped, or 
walked against a black background, in a direction 
at right angles to the axis of the lens. The 
result was a (negative) image, as represented at 
C, in which each separate attitude of the head, 
left arm, and leg can be easily distinguished. 
Such pictures provide valuable data in physio- 
logical research. In order to secure complete 
and detached pictures of birds in flight, Marey 
contrived a photographic gun (see “Gun and 


D and E. Pictures 
Obtained with Marey’s 
Photographic Gun 


107 Chrono-photography 


of a seagull. One of them is remarkable for 
showing the wings in a downward position. It 
is a curious fact that European artists seldom 
or never represent this downward stroke of the 
wing, but that the Japanese frequently do. 
Two years after Marey started his researches in 


B. Subject in Special 
Suit for Chrono- 
photography 


France, Muybridge, of California, began to in- 
vestigate the progressive movements of animals, 
his operations being carried out in the open air, 


eoCR OCC CC CHR eee ese eZ MFF Fv aeeetteeeosn 


JUSSI 33399 
\ 


WES 


C. Chrono-photograph of Subject Attired 
as at B 


as shown at F. In 1877 he erected a long shed 
containing a battery of cameras, and stretched 
in front of it, at right angles, a series of threads, 
which became broken as the subject (a man on 


F, Muybridge’s Arrangement for Obtaining Chrono-photographs 


Revolver Cameras’”’), which was of real value 
for analysing motion in such a way that the 
record could be subsequently re-compounded 
by means of the zoétrope (which see). D and E 
ate enlargements from two of a series of pictures 
obtained with this gun, representing the flight 


horseback) proceeded along the course. The 
breaking of each thread communicated elec- 
trically with the corresponding camera in the 
shed, and effected the necessary exposure just 
at that moment when the horseman was oppo- 
site the lens. A slanting fence-reflector formed 


Chrysoidine 


a suitable background for the subject, which 
was silhouetted against it, and the ground was 
covered with indiarubber to prevent dusty 
clouds flying from the horse’s hoofs, Muybridge’s 
chrono-photographs of animals in motion, espe- 
cially of the horse, gave rise to much contro- 
versy. The first thought on looking at some 
of the attitudes portrayed is that they are 
unnatural and impossible; but the matter is 
explained when it is remembered that the eye 
has a certain peculiarity not shared by optical 
instruments, namely, persistence of vision. An 
impression of everything looked at remains 
upon the retina for about one-eighth part of a 
second; and it is obvious that movements 
occutring in less time than the period named 
cannot be appreciated by the eye. In looking 
at a galloping horse the general effect of the 
movements is observed, and they are involun- 
tarily commuted into three or four positions. 
Such positions have been adopted by artists from 
time immemorial, and we have thus come to 
regard them as being correct. 

The Muybridge system of chrono-photography 


G. Marey’s Final Chrono-photographic 
Device 


was modified by Anschiitz, of Lissa, in Prussia, 
who added many new features to the apparatus 
and secured results superior to those of the 
earlier investigator. Prof. Marey, already 
alluded to, later devised a camera in which a 
roll of sensitised paper could be used, and finally 
substituted transparent celluloid film. His final 
apparatus is shown at G. A clamp H is sup- 
ported by a spring frame J. A cam K effects the 
feed motion of the film F, which is wound upon 
rollers or spools 1 and mM. By means of this 
instrument Marey was able to secure a much 
longer series of pictures than was possible with 
his earlier machines. (See also under the head- 
ing “‘ Kinematography.”’) 


CHRYSOIDINE, OR DIAMIDO-AZOBEN- 
ZENE (Fr., Chrysoidine ; Ger., Chry- 
sotdin) 

An orange aniline dye used as a light filter 
in orthochromatic and three-colour photography. 
Its formula is CsH;Ne C,H3(NH,).. The hydro- 
chloride of the base crystallises in brown octa- 
hedrons. According to Frederick Ives, it is 
possible to employ a chrysoidine filter for ortho- 
chromatic work without colour-sensitising the 
plates, but extremely long exposures are then 
necessary. 


108 Circle of Illumination 


CHRYSOSULPHITE (Fr., Chrysosulfite; Ger., 
Chrysosulfit) 

A preparation of magnesium picrate intro- 
duced by Lumiére as an addition to developers, 
so that plates could be used in daylight. Chryso- 
sulphite No. 1 contains 100 parts«of anhydrous 
sodium sulphite and 50 parts of magnesium 
picrate. No. 2 contains 100 parts anhydrous 
sodium sulphite and 15 parts magnesium picrate. 
This preparation has found but little general 
use. The normal strength in developers varies 
from 8 to 12 per cent. 


CHRYSOTYPE 

An obsolete process analogous to the blue- 
print process, invented by Sir John Herschel in 
1842; known also as ‘‘chripotype.’”’ It can be 
best described in the inventor’s own words : 

“Paper is washed with a moderately strong 
solution of ammonia-citrate of iron, and dried. 
The strength of the solution should be such as 
to dry into a good yellow colour and not at all 
brown. In this state it is ready to receive a 
photographic image, which may be impressed on 
it either from nature in the camera or from an 
engraving (or positive) in a printing frame in 
sunlight. The image so impressed, however, is 
very faint and sometimes hardly perceptible. 
The moment it is removed from the frame or 
the camera, it must be washed over with a neutral 
solution of gold of such strength as to have 
about the colour of sherry wine. Instantly the 
picture appears, not, indeed, at once of its full 
intensity, but darkening with great rapidity up 
to a certain point, depending upon exposure 
and strength of solutions, At this point nothing 
cai surpass the sharpness and perfection of 
detail of the resulting picture. To arrest this. 
process and to fix the picture (so far at least as 
the further agency of light is concerned) it is 
to be thrown into water very slightly acidified 
with sulphuric acid, and well soaked, dried, 
washed with hydrobromate of potash, rinsed, 
and dried again.” 

Herschel later recommended developing with 
a solution of nitrate of silver instead of gold, 
and fixing in sodium hyposulphite; and other 
workers advocated the use of a solution of 
potassium iodide after developing with gold. 
The finished chrysotype pictures were of a 
purplish colour. 


CHRYSTOLOTYPE 

An early and secret process of making paper 
negatives, invented by a Mr. Whipple. He 
afterwards published an albumen process in 
which glass was used, giving similar, if not 
identical results, this leading to the supposition 
that the negatives were on a kind of albumen 


paper. 
CINEMATOGRAPH (See ‘‘Kinematograph.’’) 


CIRCLE OF ABERRATION 


The spreading of the image of a point of light 
into a disc of appreciable size. This may be 
due to spherical aberration or to diffraction. 


CIRCLE OF ILLUMINATION 
A term used to express the diameter of the 
largest circular picture produced by alens working 


Circle of Least Confusion 


at its “infinity focus,” irrespective of definition 
or equality of illumination. A lens having a 
relatively large circle of illumination as compared 
with its focal length is known as a wide-angle 
lens. The extreme range in lenses commercially 
obtainable is from a circle having a diameter 
five times the focal length of the lens, as in the 
Goerz “‘ Hypergon,” to a circle barely equal to 
the focal length, as in the Petzval portrait lens. 


CIRCLE OF LEAST CONFUSION 

The theoretically perfect lens is capable of 
sharply reproducing a point or a line, no matter 
how small or fine. In telescope and microscope 
objectives, where only rays near the axis of the 
lens are used, this condition is nearly fulfilled, 
but in photographic lenses, where approximate 
sharpness over an extended field is desired, this 
critical definition at the centre of the field is 
sacrificed in order to obtain other qualities. 
The size of the disc to which the image of a 
theoretical point is spread out by any lens is 
called the circle of least confusion, and is a 
measure of the defining or “‘ resolving ’’ power 
of the lens; in British practice, $5 of an inch 
is the maximum diameter of such a disc of which 
a “sharp ”’ picture can be composed, but latterly 
on the European Continent 53, of an inch is 
often taken as the standard of sharpness. To 
realise what this means assume that an engraving 
is composed of lines and dots 5%, of an inch in 
width; with alens having a disc of confusion of 745 
of an inch a full sized copy would have the lines 
and dots broadened out to more than +z}, in., 
but at 10 in. distance from the eyes the whole 
picture would appear to be sufficiently sharp. 
By stopping down the lens the sharpness can 
be increased until almost any desired degree is 
attained. The circles of confusion at the true 
focus are due to spherical aberration (which see), 
but they are also found in portions of the image 
which are ‘out of focus” and are easily recog- 
nised in the backgrounds of portraits. In this 
case they are due to the plate cutting the cone 
of rays at some distance from the point of sharp 
focus. 


CITOCHROME (Ger., Citochromie) 

A process of four-colour printing from half- 
tone blocks, invented by Dr. Albert, of Munich. 
The black or grey plate is printed first, and then 
the yellow, red, and blue, but the solid parts of 
these colours, which would in the ordinary process 
print over each other and imperfectly produce 
black, are cut out during the Pate oa of making 
the plates, so that the black first printed shows 
through the three-colour impressions and prints 
as pure black. The inventor claims that by this 
means more rapid colour printing can be done, 
as there is no waiting for the solid colours to dry 
before each successive colour is superimposed. 
In carrying out the process continuous tone 
negatives of the colour separations are made, 
and also an orthochromatic negative of the black. 
A positive is prepared from the latter. The con- 
tinuous tone negatives for the colour separations 
are put in a special printing frame, together with 
the positive of the black plate and a ruled screen, 
the whole being in contact with a sensitised zinc 
plate. Either the frame or the arc light is made 
to describe a circular path in a vertical plane so 


109 


Clamp 


as to spread the light passing through the ruled 
screen, The positive of the black plate has the 
effect of stopping out the dark parts of each 
negative. The negative of the black plate is, 
of course, made without the positive plate being 
superposed. 


CITRATES IN DEVELOPMENT 

Alkaline citrates have been recommended as 
restrainers in dry-plate development in place of 
potassium bromide. The consensus of opinion 
is that bromide is better than any citrate if 
added to the developer before it is applied to 
the plate, but that citrates (particularly ammo- 
nium citrate) act better as restrainers when 
once development has begun. If added in suffi- 
cient quantities, citrates correct over-develop- 
ment better than bromide, and have the advan- 
tage that, after they have been added to the 
developer, density can be obtained without 
further fogging, though the development of 
detail has stopped. If ammonium citrate itself 
is used—or, in fact, the citrates of either potash 
or soda—the usual quantity required to be 
effective is from 6 to 12 gts. per ounce of 
developer; but obviously more or less can be 
used. The ammonium citrate is the most 
widely used and appears to work well with all 
developers, but when potash or soda is used 
as the alkali in a developer the citrates of potash 
and soda are to be preferred. 


CITRIC ACID (Fr., Acide 
Citronensdure) 

Occurs in colourless and odourless crystals, or 
amorphous powder, and has a strong acid lemon- 
like flavour. C;H,07H2O. Molecular weight, 210. 
Easily soluble in water, either cold or hot, slightly 
soluble in ether, and still less so in alcohol. It 
is hygroscopic, and should be kept in a well- 
corked bottle. Aqueous solutions of citric acid, 
and all other alkaline citrates, develop in course 
of time a fungoid growth, due to Saccharomyces 
mycoderma, with decomposition into carbonic 
acid and water. Citric acid is used in some 
developers as a preservative and in others as 
a restrainer, for making acid fixing and clearing 
baths, and as a preservative in emulsions, 


CITRO-CHLORIDE PAPERS 
Another name for gelatino-chloride printing- 
out papers (which see). 


CLAMP (Fr., Crampon, Agrafe ; Ger., Klampe) 

There are several kinds of clamps used in 
photography. The lantern-slide clamp is in- 
tended for holding the slide and cover glass firmly 


citrique ; Ger., 


Clamp for General Use 


together while binding. The etcher’s clamp is 
used when etching copper plates face downwards 
in the ferric perchloride bath ; it is made of oak 
thickly varnished. Various kinds of clamps are 


Claryifying 


employed in chemical operations, for supporting 
burettes, test-tubes, retorts, etc. Fretwork 
clamps (see illustration) are cheap and are often 
useful to secute photographic apparatus in 
unusual situations, to support backgrounds, or 
to improvise temporary accessories. Clips (which 
see) are occasionally wrongly referred to as 
clamps. 


CLARIFYING 


A term applied usually to the mechanical 
clearing of a solution by allowing a precipitate 
to settle or by causing more rapid precipitation 
by the addition of some inert substance to carry 
down a precipitate which does not easily sub- 
side. It is occasionally used to obtain clear 
solutions of varnishes, when an inert powder 
like pumice or chalk is added. 

In process work, the fish-glue that is used must 
undergo a process of clarifying, and “ clarified 
fish-glue’”’ is obtainable as a commercial pro- 
duct. Formerly, process workers had to clarify 
the glue themselves, and some still prefer to do 
so. It is done by adding an equal quantity of 
albumen and heating the glue to boiling-point, 
stirring well the whole time, and boiling for one 
minute. The albumen coagulates and holds the 
suspended matter, which can then be filtered 
out. 


CLAUDE LORRAINE GLASS 

A convex mirror of black glass, commonly 
known as a “ Lorraine mirror,” or ‘‘ Claude glass.” 
It was used by Claude Lorraine, the famous French 
painter, nearly three centuries ago as a means 
of reducing the view and at the same time 
modifying the colours. Used in photography, it 
is of service in showing how a view will look 
when reduced and, to a certain extent, when 
reproduced in monochrome. Used in cloud 
photography, it facilitates the obtaining of the 
mecessaty contrast between the clouds and the 
blue sky, owing to the fact that the black glass 
does not reflect the whole of the ultra-violet 
light. A convex glass, silvered but not black- 
ened, is used on the reading desk by lecturers 
to reflect the lantern pictures shown on the 
screen, and to reproduce them in miniature for 
personal reference while speaking. 


CLAUDET, ANTOINE JEAN FRANCOIS 

Born in France, 1796; died in London, 1867. 
One of the earliest workers and improvers of 
the Daguerreotype process in England, and one 
of the last to use it professionally. In 1840 
there were only two photographic establish- 
ments in London, those of Beard and Claudet. 
Claudet was also a partner in the firm of Claudet 
and Houghton (1834). In addition to improving 
the Daguerreotype process by the employment 
of chlorine vapour to increase the sensitiveness, 
he, in 1844, took out a patent for the use of red 
light in the dark-room. One month before his 
death his studio in Regent Street was burned 
down, and all his valuable daguerreotypes, pic- 
tures, and papers destroyed. 


CLAYBOARD 

A cardboard thickly coated with a chalky 
enamel and used by artists for drawing upon. 
The chalk surface permits of high lights to be 


Ito 


Cleaning Dishes 


scraped out and white lines to be cut through 
the blocks. This board may be sensitised with 
silver nitrate for printing under a negative so 
as to form a basis for drawing on. The surface 
is first prepared with arrowroot and ammonium 
chloride in the usual way adopted for sensitising 
plain papers. 


CLEANING BOTTLES 

The methods employed for cleaning bottles 
will depend upon what the bottles have contained. 
The simple and old-fashioned method of half- 
filling the bottle with water and adding sand, 
cinders, or shot may serve in some cases, as 
may the use of a little vinegar and broken-up 
egg-shell. Generally, however, the best bottle- 
cleaning solution is one made in the proportion 
of from 2 oz. to 4 oz. of hydrochloric acid to 
one pint of water. This mixture is allowed to 
remain for a timein the bottle, shaken frequently, 
poured into another one, and the bottle rinsed 
well with clean water. Bottles that have contained 
oilshould be rinsed first with a strong solution of 
household washing soda, caustic soda or potash, 
or liquor ammonie, and finally with weak hydro- 
chloric acid. Commercial benzole may also be 
used for greasy bottles, followed by a strong 
solution of washing soda, finally rinsing with 
plenty of water. 

Bottles which have been used for varnish may 
be cleaned by rinsing with liquor ammonize 
I part, methylated spirit 10 parts, and finally 
with weak ammonia and water. It is better 
to use liquid than mechanical cleaners (sand, 
shot, etc.), which are apt to roughen the insides 
of the bottles, such roughness causing them to 
become dirty and unsightly very quickly. 
Bottles used for gold toning solutions quickly 
become dirty owing to the gold depositing itself 
upon the inside of the bottle; if the deposit is 
not removed the gold in fresh solutions will be 
attracted by it, to the detriment of the solu- 
tions. Weak hydrochloric acid should be used 
as a cleaner for such bottles, and if this fails 
aqua vegia should be used. 


CLEANING DAGUERREOTYPES (See 
“‘ Daguerreotypes, Cleaning and Restoring.’’) 


CLEANING DISHES 


Dishes used for ‘‘ hypo” should not be put to 
other photographic purposes, even after clean- 
ing, as any print treated therein is liable to be 
stained. Dishes used for developing and toning 
soon become dirty, particularly when the de- 
veloper oxidises quickly, as pyro, for example. 
All dishes require to be cleaned at intervals, but 
those made of porcelain appear to require the 
most cleaning. There are two kinds of stains, 
those which appear on the surface of the glaze, 
and those which find their way under the glaze 
into the very substance of the dish, from which 
it is almost impossible to remove them. A 
solution of hydrochloric acid will remove most 
surface stains without damaging the dish, the 
method being to pour water into the dish and 
add hydrochloric acid until the solution is strong 
enough ; commercial spirit of salt will do equally 
well and is cheaper. An old tooth-brush, or 
a rag tied to a stick, may be used for the corners, 
it not being advisable to use the fingers. Fresh 


Cleaning Lenses 


stains will not require to be rubbed. For obsti- 
nate stains, mix together 8 oz. of pearl-ash, 4 0z. 
of quicklime, and 1 pint of water, stir up and 
place in the stained dishes; allow to remain for 
one hour, pour out, rinse with very dilute hydro- 
chloric acid in order to destroy the last traces 
of the pearl-ash and lime, and finally wash well. 
However, spirit of salt is more generally used, 
and it makes dishes chemically clean enough, 
even if it does not entirely eliminate the stains. 

To remove slight stains from fragile dishes, 
rub damp salt on them with a piece of flannel, 
or rinse with very dilute hydrochloric acid and 
then rub with salt. 


CLEANING LENSES 

It is easy to damage a lens by improper 
cleaning, optical glass being generally much 
softer than other kinds. Apart from actual 
scratches the surface is liable to become dulled, 
a condition that affects the “‘rapidity.” The 
necessity for frequent cleaning is obviated by 
fitting all lenses with caps to both front and 
back combinations, or by keeping them in air- 
tight cases. When a lens requires cleaning it 
should first be dusted with a camel-hair brush or 
tuft of cotton-wool, and then carefully wiped 
with a very soft silk or linen handkerchief, or 
with a soft wash-leather. If the surface still 
appears cloudy, a single drop of pure alcohol 
should be put on each of the surfaces, which should 
be carefully wiped until quite dry. The spirit 
must not be allowed to run between the lens 
and its brass cell, and care must be taken not 
to remove the dead black coating from the lens 
cell. The edges of the lens in contact with the 
cell are best cleaned with the pointed end of a 
bit of soft wood over which the rag is stretched. 
Dr. Miethe recommends the use of pith, such 
as that of the rush or elder, for this purpose. 
A lens that has become scratched or dulled 
should be sent to the maker to be repolished. 
The greatest mistake an amateur can make is 
to attempt to repolish a lens with rouge, putty- 
powder, etc.; even the maker cannot repolish 
a badly scratched lens so that it will work quite 
as well as when it was new, therefore the result 
of unskilled work can easily be anticipated. A 
lens should not be wetted if it can be avoided, 
and in the case of condensation of steam or dew 
upon the surfaces, the moisture should be re- 
moved as quickly as possible. 


CLEANING NEGATIVES 

The films of negatives are best cleaned when 
wet. Usually they are merely wiped over with 
a piece of wet cotton-wool; but to remove a 
dirty or messy appearance from a dry negative 
use cotton-wool soaked in methylated spirit, 
rubbing very lightly to avoid reducing the den- 
sity. The metal-polish reducer (see ‘‘ Baskett’s 
Reducer’’) may also be used for cleaning the 
dried film, but must be used very gently. 

It is generally the glass side, not the film 
side, of a negative that requires cleaning. In 
the process of manufacture some stray emulsion 
may get on the glass side, which, if allowed to 
temain, would show in the print. Emulsion 
streaks are best removed when wet by rubbing 
with damp table salt; but the same method 
answers when the negatives are dry. 


III Clips 


To clean off the films from “‘ waster” nega- 
tives that have been varnished, soak them in 
a hot solution of soda or potash, and then rub 
with a stiff scrubbing-brush, finally rinsing ; if 
potash is used, do not let it touch the fingers. 
Soaking in water containing a little nitric acid 
answers for unvarnished negatives, scrubbing 
or scraping afterwards if necessary. The follow- 
ing solution is also recommended for removing 
unvatnished films: Citric acid 1 oz., hydro- 
chloric acid 2$ 0z., water 20 oz. Soak in this 
for an hour or two, scrub, and finally rinse. 

An excellent cleaning and polishing mixture 
for glass consists of the following :— 


Rain or soft water. ene OR, 
Powdered pumice-stone . Het ee 
Whiting or prepared chalk 13 ,, 
Liquor ammoniz ; 4 5, 


Apply with a piece of chamois leather or flannel, 
and polish with a clean rag or soft paper. 


CLEARING SOLUTIONS 

Used for removing development stains from 
negatives or prints. When the staining is due 
to insufficient sodium sulphite in the developer 
the following formula is recommended :— 


Alum : ‘ T Of. 55 g. 
Hydrochloric acid . + I2 ccs. 
Water . a AO cg oy BO0O* 5 


The plate should be well rinsed from the 
developer, immersed in this clearing solution 
for two or three minutes, and then washed for 
fifteen minutes and fixed as usual. The use of 
an acid fixing bath renders a clearing solution 
unnecessary. For clearing development fog, or 
chemical fog, or staining caused by the plates 
or paper being stale, a solution of thiocarbamide 
is the best to employ. (See under the heading 
of “ Fogged Negatives, Treatment of.” Lantern 
slides are treated as described under their own 
heading.) 

In process work, clearing solutions are used 
to remove any deposit of silver from between 
the dots of half-tone negatives, and also to 
sharpen up the dots. This process is called 
“cutting.” For dry plates, ferricyanide and 
“hypo” (Farmer’s reducer, which see) is used, 
and for wet plates, iodine and cyanide. 


CLERK-MAXWELL, JAMES 

Born at Edinburgh, 1831; died at Cambridge, 
1879. First Professor of Experimental Physics 
at Cambridge (elected 1871). He made fe- 
searches into the composition and vision of 
colour, the kinetic theory of gases, electricity, 
etc., and was associated with the early experi- 
ments in colour photography, with regard to 
which he made, about 1861, many suggestions, 


CLICHE 

The French term, now anglicised, applied to 
electrotypes, stereotypes, and process blocks. 
Also used sometimes to indicate negatives and 
positives. (See also “ Block.’’) 


CLIPS (Fr., Pinces ; Ger., Klammern) 

Spring clips of various kinds are used for 
hanging up wet prints or films. The American 
wood clip A is useful for many purposes; clothes 


Clip Copyboard 


“ negs” of practically identical shape are obtain- 
able at a very cheap rate. Metal clips B are 
obtainable in variety. Such clips are especially 
useful for suspending sensitised carbon tissue 
or photo-lithographic paper for drying. Split 


A. Wooden Clip 


B. Metal Clip 


cotks with rubber bands make good clips for 
some purposes (see an illustration referred to 
under the heading ‘‘ Film Manipulation’’). Nega- 
tive clips, or plate-holders, are used for holding 
and lifting negatives during development, wash- 
ing, etc., to avoid touching them with the 
fingers. Film-developing clips are intended for 
holding the ends of roll-films when developed 
in the length. 


CLIP COPYBOARD 

A board used in process work for holding the 
original for copying ; it is provided with spring 
clips instead of with pins. In one type the 
clips slide in grooves, whilst in another they 
are inserted in holes, and large clips to hold 
books and small clips to hold paper or card- 
board are provided. 


CLOCK, DARK-ROOM (Fr., Horloge de 
laboratotve ; Ger., Dunkelzimmer Uhr) 

A clock specially made to facilitate the timing 
of photographic operations. The Watkins dark- 
room clock, a former pattern of which was 
known as the eikronometer, is primarily designed 
for factorial development. It has two hands, 
one completing a revolution in one minute, 
while the other takes ten minutes. A stop 
motion permits both hands to be started from 
zero as the developer is poured on the plate, and 
an outside indicator marks the completed time. 
The Welborne Piper stop clock is for factorial de- 
velopment, and for timing numerous other mani- 
pulations, in addition to which it has various 
novel and useful movements, 


CLOTH, BOLTING (See “ Bolting Cloth.”’) 


CLOTH, FOCUSING (See “‘ Focusing Cloth.’’) 


CLOUD NEGATIVES 

Clouds that are to be added to landscapes must 
be taken under similar conditions to those of 
the landscapes for which they are required. A 
large common or open space should be selected 
for photographing, so that a low horizon line 
may be included on the plate. And this low 


112 


Clouds, Printing in 


horizon line should be as unbroken as possible. 
The formation of clouds near the horizon is 
different from that at higher altitudes, and it 
is therefore necessary that clouds near the 
horizon should be included on the plate so that 
they may appear correct if the formation of 
the landscape picture necessitates showing 
sky near the horizon. Clouds taken right 
opposite the sun, or directly towards it, are 
quite useless for adding to the large majority 
of landscape pictures, as most landscapes are 
taken with an oblique front lighting. Clouds 
should therefore be photographed with a similar 
lighting. If the sun should be in the south at 
the time of photographing clouds, those about 
the north-west and north-east will be the most 
useful. As opportunities offer, cloud negatives 
should be taken with different lighting, and of 
varied character; brilliant piled-up masses, rain 
clouds, broken-up skies, quiet, calm, summer 
effects, etc., so that a suitable negative can be 
be selected when it becomes necessary to add 
clouds to a cloudless landscape. It is necessary 
to study the arrangement or grouping of the 
clouds on the plate so as to get the principal 
point of light, or the principal feature in the 
grouping, towards one side of the plate. The 
grouping must be such that it can be utilised in 
assisting the formation or composition of a pic- 
ture whenever practicable. The principal cloud 
masses should form an angular line across the 
plate. The exposure for cloud negatives must 
be very short, ranging from one-sixtieth of a 
second for very light clouds, up to one-fortieth 
for heavy masses, using a rapid plate (200 H. 
and D.), and lens aperture f/16 at mid-day in late 
spring or early summer. Development may be 
normal, With such short exposures the nega- 
tive will be thin, and suitable in every way for 
printing into landscapes. 


CLOUD SHUTTER (See 
Shutter,’’) 


CLOUDS, PRINTING IN | 
The landscape or marine picture should be 
printed first and the clouds added subsequently. 
No attempt should ever be made to block out 
the sky on the landscape negative, even if it 
should print to a pale grey tone. Painting out 
a sky leaves the outlines of the distance hard 
and crude, instead of delicate and soft, as they 
invariably appear in a landscape print, even if 
sharply defined throughout. It is no disad- 
vantage to print a sky over a pale tone of grey ; 
the clouds are softened in their contrasts, and 
frequently harmonise better with the tone of the 
landscape. At times, the grey tone of a sky 
may be a disadvantage when it is desired to 
add a sky that should be as brilliant as possible 
for a special effect. In that case the sky may be 
kept white by shielding. A card is roughly cut 
to the shape of the outline of the landscape, and 
supported over the sky part of the picture during 
printing, the edge of the card being directly over 
the outline of the landscape. This plan allows 
the landscape to print fully, but the sky will be 
vignetted off from its full printing, where it joins. 
the landscape, to a pure white for the greater part 
of its area. The suddenness or the gradual 
nature of this vignetting will be determined by 


** Foreground 


With Isochromatic Plate and Medium (“‘ Three Times ’’) 
Screen 


With Isochromatic Plate, but Without Screen With Isochromatic Plate and ‘* Six Times ”’ Screen; 
over-corrected 


VARIOUS RENDERINGS OF DAFFODILS IN BLUE VASE 


he 


Clouds, Printing in 113 


the distance of the card from the surface of the 
negative. When the landscape print is obtained, 
a mask is also required, to be used to shield it 
from the action of the light while the clouds are 
ptinted. The most satisfactory method of 
obtaining this mask is to take a rough silver 


we 


- Aand B. Landscape Negative and Mask 


print of the landscape, and cut it carefully to 
the outline of the subject. Any small dark 


objects, such as a church spire, the branches. 


and twigs of a leafless tree, may be disregarded 
in cutting this mask, as the clouds may be printed 
over them. But the mask must be cut so as to 
shield any light object, excepting in special 
cases which must be determined on their merits. 
The landscape and mask are shown at A and B. 
The landscape print must be placed in position 
behind the cloud negative, care being taken that 
the horizon of one is near the horizon of the other, 
so as to ensure that the cloud forms are in correct 
relation to the landscape. The clouds must be 
printed in a frame one or two sizes larger than 
the landscape, the frame being provided with a 
sheet of plain glass so that the smaller negative 
can be printed without difficulty. The large 
frame allows space for arranging the landscape 
print in the correct position on the cloud negative 
irrespective of the extent to which it may project 
in any direction. 

If a large number of prints are required from 
one negative, the most satisfactory manner of 
using the mask is to attach it permanently to a 
piece of glass the same size as the print. If only 
a few are wanted, the mask may be wetted 
sufficiently to render it quite limp; it will cling 
to the glass thoroughly satisfactorily, without 
risk of movement, while the sky is printed. In 
either case, the mask is adjusted in position on 
the outside of the plain glass in the printing 
frame when everything is ready for printing the 
clouds. The frame should be in a horizontal 
position. . 

The mask should be carefully adjusted so that 
it overlaps the landscape very slightly, about 
one-sixteenth of an inch, or less in small work 


Cand D. Diagrams Showing How Carbon and 
Bromide Prints are Marked for Masking 


The fact that there are two thicknesses of glass 

between the mask and the print—the plain glass 

of the frame and the sky negative—will cause 

the mask to print with a soft or vignetted outline, 

and this slight overlapping is to compensate for 

the manner in which the light diffuses under the 
8 


Clouds, Printing in 


mask, and it prevents the print from showing 
any hard junction. In addition, a card should 
be supported over the landscape portion, as 
shown at E, while the clouds are being 
printed; this card should project over the sky 
to a small extent to soften off the depth of 
printing near the horizon. The extent and 
nature of this softening will be determined by 
the extent to which the card projects beyond 
the landscape and its height above the surface 
of the negative. The edge of the card may be 
either straight or cut approximately to the out- 
line of the landscape, according to the subject. 
This vignetting off towards the horizon becomes 
absolutely necessary when a grey sky has been 
vignetted into a plain white, as described 
earlier. 

All preliminary work in cloud printing should 
be on silver printing-out paper. Working by 
daylight in a process that gives a very strong 
image enables the work to be followed easily. 
The mask can be adjusted to the correct position 
without any difficulty, and any error in adjust- 
ment or in arranging the card shield can be seen 
at almost the beginning of printing, and rectified 
immediately. The experience gained by print- 
ing clouds in silver will enable any photographer 
to place the masks and shields correctly without 
difficulty when adding clouds to platinotype 


E. Shielding Part of Negative when Printing 


carbon, or bromide prints, though in these pro- 
cesses there is no strong image to act as a guide. 

The method of working in platinotype and 
carbon, inasmuch as they are daylight processes, 
will be similar to that described for silver print- 
ing, but there is no image that can be seen 
sufficiently well through the cloud negative to 
assist in correctly placing the mask. In plat- 
inotype, the image is an assistance, but it cannot 
be utilised in the same manner as in silver. 
When the landscape printis taken from the frame, 
a small pencil mark is made at each end of the 
print, at the exact point to which the mask 
has been cut; and about an eighth of an inch 
above each mark, a second one is made to serve 
as a guide in placing the mask. These pencil 
marks are shown at EE. When the landscape 
is being arranged under the cloud negative, 
these pencil marks are of great assistance in 
securing the correct position. But their great 
value consists in the manner in which they 
enable the correct placing of the mask to be 
determined. They are plainly visible through 
the cloud negative, and the mask can be fitted 
to them as easily as to the strong image of a 
silver print. It is self-evident that if the mask 
is in the correct position at the two margins it 
must be in the correct position throughout its 
length. The exposure should be timed by 
means of an actinometer. 

In carbon prints there is no image whatever 


Coal-tar Colours 


to serve as a guide for marginal marks, and their 
position must be determined differently. A 
little water-colour is required—white or light 
yellow—and a fine brush. When the print isin 
the frame, either before or after the exposure, 
one-half of the back of the frame is opened, and 
a fine mark is made on the margin of the negative 
at the spot corresponding with the mask, That 
half of the back of the frame is at once closed 
again so as to press the tissue on to the negative, 
and the moist colour will set off on to the margin 
of the print. While this half remains closed, the 
other half is opened and a similar mark made on 
the margin of the negative at the correct position 
for the mask. The precaution should be taken 
of opening each half separately a second time to 
ascertain that the colour has been transferred 
to the face of the tissue; and, before removing 
the print, a mark should be made on the back 
to indicate which is the top. The exposed tissue 
should then be removed from the frame, the 
marks strengthened, and a second mark made 
just above each to correspond with the pencil 
marks in platinotype. With these marks the 
correct placing of the mask is easy, and this and 
the printing will be the same as described for 
platinotype. The appearance of the carbon 
print is shown at C, the white brush marks F F 
corresponding to HE in diagram A. 

In bromide printing, the method of working 
is the same as in carbon, but a dark colour must 
be used for the brush marks, black or dark-brown. 
Diagram D illustrates a bromide print to be used 
with the mask B, the brush marks being indicated 
at GG. In bromide printing, the card shield 
must be kept moving during the exposure, to 
prevent a sharp line from appearing. 

In enlarging by means of a lantern, pencil 
marks can be made on the enlargement, the 
image thrown by the lens forming the guide. 
The card shield may be held in any convenient 
position between the lens and the enlarging 
easel so as to shield the landscape, and it must 
be kept in motion throughout the exposure of 
the cloud negative. 


COAL-TAR COLOURS 
Coal-tar, Colours.”’) 


See “Aniline, or 
> 


COATING 

It will be found somewhat easy with a little 
practice to coat plates if the operation is prac- 
tised first in daylight or gaslight, and for this 
purpose it is advisable to start with whole 
plates, assuming that one wishes subsequently 
to obtain quarter plates. A pneumatic holder 
(which see) should be obtained, and the sheets 
of glass thoroughly cleaned and stacked, with 
the surfaces to be coated away from the operator. 
The emulsion should be at a temperature of 
95° F. (35° C.) in summer and 98° F. (36°6° C.) 
in winter; and if the room is cold the glass 
itself should be warmed. ‘The pneumatic holder 
is taken in the left hand, the bulb well squeezed, 
and the lip of the holder just wetted and then 
pressed on to the back of a sheet of glass in the 
centre and the pressure relaxed. The suction 
—really the pressure of the atmosphere on the 
surface of the glass—holds it firmly against 
the holder, wherein there is a partial vacuum. 
The glass should then be held horizontally, and 


114 


Coating 


the emulsion poured on to the middle, prefer- 
ably from an earthenware teapot which has a 
spout that starts from near the base, as this 
avoids the air bubbles which rise to the top of 
the emulsion. Failing a teapot, the ordinary 
invalid’s feeding cup would be a good sub- 
stitute. 

The pool of emulsion should be poured on 
to the centre of the plate, and, as soon as it 
covers about half the area, the plate should be 
tilted so as to cause the emulsion to run to the 
top tight-hand corner, then to the top left-hand 
corner, then to the bottom left-hand corner, 
and finally to the bottom right-hand corner, 
and the excess drained off here. This must be 
done slowly, otherwise the emulsion will run 
over the edges; and it is advisable to practise 
over a good-sized dish so as to catch any spillings. 
As soon as coated, the plate should be slid on 
to a sheet of plate glass accurately levelled, and 
allowed to set. 

The coating of paper is not so easy, but it 
may be done by pouring the emulsion into a 
dish, tilting this, and drawing the paper over 
the top of the emulsion. At least a yard of 
paper can be coated in this way, and with care 
but few bubbles will arise. But by far the 
simplest plan is to use one of the film develop- 
ing dishes provided with a roller. Having the 
paper cut in long lengths, pass one end round 


Tilted Dish of Emulsion for Coating Paper 


the roller, and, keeping it tightly strained against 
the latter, pour in enough emulsion to cover a 
little less than half the diameter of the roller. 
Then the paper can be drawn through the emul- 
sion and straight up, and enough will cling to it 
to give good results. Naturally, the emulsion 
must be kept hot. 

Commercially, of course, special machinery is 
used both for plates and papers, and in the 
former case the cleaned glasses are fed on to 
the bed of the machine and coated with emulsion 
by various devices. Thence the glasses pass 
through an ice tunnel, which thoroughly sets the 
emulsion, and at the other end of the machine, 
which may be 30 ft to 40 ft. from the coating 
end, they are stacked in racks by hand and 
thence conveyed to the drying-room. 

The commercial paper-coating machinery is 
usually arranged so that the paper, which is in 
long reels, passes round a roller through the 
emulsion. The coating is chilled either by a 
cold roller or by cold air; the paper then 
passes on, is formed into loops or festoons, 
and traverses the drying-room, being agaip 
reeled at the other end. 

In process work, coating is an important 
operation, For collotype, the gelatine coating 
is applied by levelling the glass plate and pour- 
ing on a measured quantity of solution, guiding 
it to the edges by means of a catgut bow or a 


Co-axial 


glass rod. For coating zinc or copper a whirler 
(which see) is invariably used, the coating being 
evenly spread by centrifugal force, while the sur- 
plus is thrown off. In the case of very volatile 
mediums, such as bitumen, it is sometimes the 
practice to coat by pouring on the solution with 
a sweep of the bottle along the top edge of the 
plate, taking care to incline the plate so as to 
allow the solution to run down and the surplus 
to run off, 


CO-AXIAL 

Having a common axis. Thus the positive 
and negative elements of a telephoto lens or the 
eyepiece and object glasses of a telescope or 
microscope are said to be co-axial. 


COBALT BLUE (Fr., Bleu de cobalt; 
Kobaliblau) 

A compound of alumina and oxide of cobalt 

used in painting ; of slight photographic interest. 


COBALT CHLORIDE (Fr., Chlorure de cobait ; 
Ger., Kobaltchlorid) 

Synonym, cobaltous chloride. CoCl, 6H,O. 
Molecular weight, 238. Solubilities, soluble in 
water and alcohol. Ruby red crystals, obtained 
by dissolving cobalt carbonate in hydrochloric 
acid and evaporating. The addition of small 
quantities of cobalt chloride to printing-out 
emulsions produces greater contrast. 


COBALT SALTS, PRINTING WITH 


Cobalt belongs to the same group of metals 
as iron and manganese, and, like these, many of 
its salts are sensitive to light. Although no 
practical process has so far been founded on 
this fact, it is as well to record briefly the 
researches of A. and I,. Lumiére on the subject. 
The most promising salt is obtained by dis- 
solving cobaltic oxide, Co,O3, to saturation in 
oxalic acid solution, or by precipitating cobaltic 
oxyhydrate from a cobaltous salt solution by 
means of sodium peroxide and dissolving the 
precipitate, after careful washing, to saturation in 
oxalic acid solution, the cobaltic salt being kept 
all the time in excess. This operation must be 
performed in the cold, and takes some hours. A 
green solution is obtained which can be used 
to sensitise gelatinised paper, and, after drying, 
on exposure to light under an ordinary negative, 
a pale rose-coloured image of a cobaltous salt is 
obtained. The action is extremely rapid, taking 
but a fraction of the time necessary to print 
under similar conditions with a silver salt. The 
print, when ready, should next be immersed in a 
5 per cent. solution of potassium ferricyanide 
and washed. The image thus obtained is a pale 
rose colour and not very intense, consisting of 
cobalt ferrocyanide. This may be toned with an 
alkaline sulphide, which produces dark brown 
cobalt sulphide. By treatment with an iron salt, 
a blue image is obtained; a nickel salt gives a 
red image. Attempts to develop the cobaltous 
image with organic compounds (see ‘‘ Manganese, 
Printing with’’) were not satisfactory, in all 
cases it being found much more difficult, and 
the only substances proved to be of any value 
were hzematoxyline, which gave a violet blue 
image that was changed to reddish by hydro- 
chloric acid, and benzidine, toluidine, and their 


Ger., 


115 


Cockling of Prints 


hydrochlorate salts. These produced on the 
places not affected by light, so that they would 
give a negative print from a negative, an intense 
blue image, which was turned brown by ammonia 
and pale yellow by hydrochloric acid. 

Further researches with the citrate, stannate, 
nitrite, tartrate, gallate, and sulphocyanide of 
cobalt have been made, but the results were still 
less promising. 


COBALT-LEAD TONING 

A process for toning bromide and gaslight 
prints to a green colour, introduced by MM. 
Lumiére and Seyewetz in 1905. Two solutions 
are required :— 


A. Potassium ferri- 
cyanide . . 144 gs. 65 g. 
Lead nitrate Pr << abe 7 ae 
Water : 5 Oz 1,000 ccs. 
B. Cobalt chloride . 4,, IIo g. 
Hydrochloric acid 13 ,, B302- 
Water e : rate 1,000 ccs, 


For vigorous greens fully developed prints 
must be used. The print is placed in A until 
bleached, is next washed very thoroughly, and 
then immersed in bath B. The image on the 
finished print is made up of lead, silver, iron, and 
cobalt in the form of a ferrocyanide and of the 
chlorides of silver and lead. If the toning action 
is prolonged, the cobalt will completely replace 
the silver and lead. 


COCKLING OF PRINTS 

Photographs mounted in a wet state upon thin 
cardboard, or upon the leaves of an album, 
invariably cockle or curl when dry, whereas 
prints mounted surface-dry do not cockle so 
badly. The defect is due to uneven expansion 
caused by the wet mountant, and can be made 
worse by unskilful manipulation. Careful selec- 
tion of the mountant minimises the trouble, and 
the following formula is as good as any in this 
respect :— 


White dextrine : 1/360 grs; < $2.2. 
Powdered alum ; « PREG Petes, 
Sugar. . : ae as? Bakes iy ig 
Hot water ‘ 1 OZ. 100 ces, 


This, when thoroughly mixed, should form a 
thick cream, which should be allowed to stand 
a day before use. Take the trimmed dry print 
and lay it face downwards on a sheet of glass, 
and with a fairly stiff brush apply the smallest 
possible quantity of mountant to the back of 
the print, distributing evenly and quickly ; 
before the mountant has had time to soak 
through, place the print upon the mount and 
squeegee or rub down. Place two or three 
thicknesses of fluffless blotting-paper over the 
picture and mount, and put into a copying press 
and screw down hard, or put under heavy pres- 
sure for several hours. When dry, there should 
be little or no cockling. 

Another plan is to brush the back of the dry 
print over with a strong solution of gelatine or 
soft glue, and to damp slightly the mount before 
placing the print in position, drying under 
pressure. 

The theory of the subject is to prevent 


Coddington Lens 


expansion of the print before pressing it in 
contact with the mount; or, if this expansion 
is unavoidable, to expand the mount, as in the 
preceding paragraph, and let mount and print 
contract together. Another point is to use a 
thoroughly even mountant, because should one 
part of the print get wetter than another, cockling 
is almost sure to occur. 

Photographers may learn something from the 
draughtsman’s method of stretching drawing 
paper, and even if it is dangerous to mount 
prints in this way, they can adopt it when pasting 
brown paper on the backs of photograph frames. 
The draughtsman slightly damps the back of 
the paper, thus evenly expanding it all over, 
touches the margin all round with paste, and 
“lays”? the paper on the board, thoroughly 
pressing the margin into contact. The paper 
contracts in drying and becomes as tight as a 
drum-head. 


CODDINGTON LENS 

A biconvex spherical lens with a deep groove 
filled with an opaque substance running round 
the centre. The groove acts as a diaphragm. 
This lens is used as a hand magnifier, and gives 
a large, bright field, but its working distance is 
short. 


COERULINE S§ (Fr. and Ger., C@ruline S) 

Synonyms, ccerulein, coerulean. A compound 
of alizarine blue and sodium bisulphite, which 
has been occasionally used for colour-sensitising 
plates. 


COFFEE PROCESS 

A mixture of coffee, advocated by Colonel 
Baratti, used as a preservative in the early days 
of the dry collodion plate. About 1855 there 
wete numerous announcements of new pre- 
servatives wherewith the sensitive sutface of 
collodion plates could be covered, so as to enable 
them to be dried and kept ready for use. Among 
the many substances recommended and widely 
used were beer, tea, treacle, gum arabic, brown 
sugar, white sugar, raspberry vinegar, wort, 
malt, and tobacco. 


COINS AND MEDALS, PHOTOGRAPHING 

The difficulty presented by subjects of this 
character is solely due to the low relief of the 
image and the consequent absence of contrast 
in light and shade. This difficulty may be 
entirely overcome by suitable lighting. The 
coin or medal should be placed so that it receives 
a strong light from one side, the direction of 
the light being parallel with the face of the coin 
and striking the edge strongly. There may be 
a little diffused light in front, but as large a 
proportion as possible should be across the face, 
just skimming the surface. However slight the 
relief, it will be shown by strongly marked lights 
and shadows if this method of lighting is adopted, 
and the production of a successful negative will 
ome no difficulty, The exposure must be 
short. 


COINS AS WEIGHTS 

English silver coinage is minted exactly by 
weight in proportion to its value—namely, 
43647 gts. for every five shillings; thus a new 


116 ; Collimating Lens 


threepenny-piece weighs 21°83 grs., a sixpence 
43°6 grs., and so on, the sixpence and three- 
penny piece being almost exactly one-tenth 
and one-twentieth respectively of the avoir- 
dupois ounce. The list gives the approximate 
avoirdupois weights obtainable by the use of 
coins just slightly worn :— 


20 gts. = one threepenny-piece, 
40 ,, = one sixpence. 
43. ,, = one farthing. 
61 ,, = half-sovereign. 
88 ,, == one halfpenny. 
123 ,, = one sovereign. 
TAS yy 5, FF) ORO DEBBY 
176 yy =o ome toe. 
218 ,,. = half-crown. 
1 oz. = one halfpenny and one threepenny 
piece. 
34 ,, = florin and sixpence. 
i, = three pennies, or five halfpennies. 
1 lb, = forty-eight pennies. 


The United States five cent nickel coin is 
exactly 5 g. (77 gts.) in weight and 2 centimetres 
in diameter, The English halfpenny-piece is 
exactly 1 in. in diameter and weighs, when 
new, exactly one-fifth of an ounce; the penny 
is of less convenient weight—one third of an 
ounce. No halfpenny-piece is issued that is more 
than -2 per cent. wrong in weight, one-fifth of 
1 per cent. being what is known as the legal 
“remedy ” in weight, and this does not amount 
to I gr. per ounce. 

French coins ate particularly suitable as 
metric weights, namely :— 

25° Bs 5 francs (silver) 


2 ” ” 
I > x) 


4 bp) ? 

10 centimes (bronze) 
5 Pd 9? 
2 ” ”? 

| ry) I ” ” 


COLAS’S PROCESS 

A ferro-gallic printing process perfected by 
Colas, a German. It is described under the 
heading “‘ Ferro-gallic Process.” 


Oo 
Haun dun 


COLD BATH PROCESS (See “‘Platinotype.”) 


COLD, EFFECT OF 

The action of photographic chemicals is seri- 
ously retarded by cold, as explained under the 
heading “Temperatures.” 


COLD EMULSION (See “ Emulsion.”) 


COLLIMATING LENS (Fr., Collimateur ; Gery 
Kollimatorlinse, Kollimator) 

An achromatic biconvex lens placed in a 
tube at its principal focal distance from a narrow 
slit or small aperture. A collimator is used in 
lens-testing apparatus to produce a parallel 
beam of light, and in conjunction with the 
spectroscope. Another form of collimator is a 
small fixed telescope having cross-wires at its 
focus; this is employed for adjusting the optical 
axis, or line of sight, in astronomical instru- 
ments. 


ee. ¢ 23 


gyi 


Collinear Lens 117 


COLLINEAR LENS 
An anastigmat lens introduced in 1894 by 


- Voigtlander, and made in intensities varying 


Collinear Lens 


from f/4'5 to f/12°5. The illustration shows the ~ 


construction of the original type. 


COLLOCHROME 
Coloured collotype printing. 


COLLODIO-ALBUMEN PROCESS 

An obsolete process, which gave most beautiful 
transparencies. A plate is first coated with 
bromo-iodide collodion, then sensitised in a silver 
bath and washed to remove excess of silver 
nitrate. Next it is coated with a mixture of 
albumen, bromide, and iodide of potassium, 
which destroys the sensitiveness of the plate 
so that it can be dried in daylight. When 
required for use, the plate is resensitised with 
silver nitrate and thoroughly washed and dried. 
A gallic acid and silver nitrate developer is 
generally used. (For working details see ‘ Albu- 
men Process,” sub-heading “ Positives.’’) 


COLLODIO -BROMIDE (See _ “ Collodion 
Emulsion.’’) 


COLLODIO - BROMO -CHLORIDE EMUL- 
SION (See ‘‘ Collodion Emulsion.’’) 


COLLODIO-CHLORIDE 

An emulsion of silver chloride suspended 
in collodion. Generally used for printing- out 
papers. (See also ‘“Collodion Emulsion.’’) 


COLLODIO-GELATINE (Fr. and Ger., Collo- 
dio-gelatine) 

H. W. Vogel suggested that dry gelatino- 
bromide emulsion should be dissolved in glacial 
acetic acid and alcohol, and mixed with a solu- 
tion of pyroxyline in similar solvents, with the 
object of combining the advantages of the two 
processes. The process has found no practical 
use, as the sensitiveness is very low. Husnik 
gave the following formula :— 

Dry gelatino-bromide 

emulsion . ; Maas He 30 g. 

Glacial acetic acid eer Ree 30 ccs. 

Alcohol ° : ete Caen 305, 


Dissolve, and add— 


Pyroxyline . ‘ hig LORS hs Oe 
dissolved in— 
Glacial acetic acid POE OR 30 ccs 


Alcohol . 800 mins. 50 ,, 


COLLODION (Fr., Collodion; Ger., Kollodium) 

A solution of pyroxyline in a mixture of equal 
quantities of alcohol and ether; it should be 
kept in a well-stoppered bottle. It is a colour- 


Collodion 


less, syrupy liquid, being more or less fluid 
according to the quantity and nature of the 
pyroxline used. It will keep indefinitely if made 
with a good pyroxyline ; the pyroxyline should 
be first well saturated with the ether and then 
the alcohol added, and, on shaking, the cotton 
should completely dissolve. The solution should 
now be set aside in the dark and allowed to 
stand two or three days to allow any mechanical 
impurities to settle, this being preferable to 
filtration, as in this process some of the solvents 
are lost. The ether used may be the so-called 
methylated ether, and should have a specific 
gravity of :720; the alcohol may be the indus- 
trial methylated spirit, but it is preferable to 
use the pure alcohol; aqueous alcohol should be 
used when aqueous solutions of salts are to be 
added to the collodion, as is often the case in 
making collodio-chloride printing-out emulsion. 

Collodion is used for enamelling prints (see 
** Collodion, Enamel ’’) and as the vehicle for the 
silver salts in the wet-plate process, dry collodion 
plates, collodion emulsion, and collodio-chloride 
paper. 

It is important that collodion should always 
have that degree of viscosity which has been 
found the most satisfactory for the particular 
purpose. Viscosity may be. defined as the 
thickness or syrupy nature of the collodion. A 
very thin collodion—that is, one with less 
viscosity—is apt to allow the silver salts to 
deposit at the bottom of the bottle; on the 
other hand, for some purposes—such as enamel- 
ling—a less viscosity is advisable. The simplest 
method of testing the viscosity is by means of 
Von Hiibl’s viscosimeter, a glass tube 6 in. 
(15 cm.) long, 1:2 in. (3 cm.) internal diameter, 
with one end drawn into a fine aperture of 
about z; in. (1 mm.). About 4in. (8 cm.) from the 
wide end, and on the outside of the tube, should 
be scratched a line. This tube should be filled 
up to the mark with distilled water, the small 
aperture being covered with the finger, and 
by means of a stop-watch the time taken for 
the water to flow out should be noted. The 
mean of six tests should be taken. Then the 
same process should be gone through with the 
collodion to be tested; the time taken by the 
collodion divided by that taken by the water 
gives the viscosity of the collodion. For in- 
stance, assume the mean for six tests for dis- 
tilled water. at a certain temperature to be 
84 seconds, and the time for a specially thick 
4 per cent. collodion to be 187 seconds; then 
187 +84=2.226, the viscosity of the collodion. 

The proportion of alcohol and ether is not a 
fixed quantity. In summer more alcohol should 
be used, and thus the loss from evaporation 
slightly checked. For coating large plates a 
collodion rich in ether is difficult to work, as the 
solvents evaporate before the plate is covered ; 
on the other hand, a film produced by a collodion 
rich in ether is tougher. In the wet collodion 
process excess of alcohol produces greater sensi- 
tiveness, whilst in the dry collodion process the 
ratio of the solvents is of less importance, and 
certainly in those emulsions washed by precipi- 
tation an excess of alcohol is an advantage. The 
solubility of the silver nitrate and the salts has 
also considerable bearing on this point, and it 
may be considered as a general axiom that all 


Collodion Bottle 


salts are more soluble in alcohol than in ether. 
More particular details will be found under the 
special headings. 

In process work, collodion is an important 
factor on account of the facility and cheapness 
with which, by its help, negatives suitable for 
the various reproductive processes can be made. 
The comparative slowness of wet-plate exposures 
is no drawback where exposures are invariably 
made by electric light; and the development, 
fixing, intensification, clearing, and drying are 
all executed much more quickly than on gelatine 
plates. The silver deposit being on the surface, 
the image is more susceptible to intensification 
and reduction than an emulsion film. Finally, 
on the ground of cheapness, wet collodion holds 
the field. It has been calculated that the 
average cost of making negatives in half-plate 
size is: Wet collodion, 1d.; collodion emulsion, 
1fd.; dry plate, 24d. Collodion is also largely 
used in process work for stripping. (See also 
conclusion to article ‘“Collodion Process 
(Wet).”’) 


COLLODION BOTTLE (Fr., Flacon a collo- 
dion ; Ger., Kollodiumgtessfiasche) 

A long, narrow bottle for holding and pour- 
ing collodion in the wet-plate process. The 
earlier patterns had merely an ordinary stopper, 
but in the modern “‘ cometless ”’ collodion bottle 
A, so called because its peculiar construction 


B. Collodion Pouring 
Bottle and Filter 


A. “ Cometiless” 
Collodion Bottle 


ensures practical freedom from the comet- 
shaped spots and other markings incidental to 
wet-plate work, a closely-ground cap is sub- 
stituted. A combined pouring bottle and filter 
is shown at B. A piece of muslin or cotton is 
tied over the lower end of the inner tube, through 
which the contents must pass before being poured 
out. The surplus is returned to the bottle 
through a notch at the side of the tube. For 
a third type of bottle, see under the heading 
‘*‘ Collodion Filter.” 


COLLODION EMULSION 


A suspension of various silver salts in collo- 
dion, and used for printing-out papers, trans- 
parencies by development, and negative work. 
The simplest of all collodion emulsions to make 
is that for printing-out paper, or, as it is some- 
times called, collodio-chloride paper. There are 
numerous formule, but those given in the next 
column and in the first column of p. 119 have 
been found of great practical use. 


118 


Collodion Emulsion 


Valenta’s Formula 


Lithium chloride o9 g. 
Strontium chloride ; ‘ A ae 
Absolute alcohol IO ccs 
Glycerine ‘ ‘ : ID 4 


Dissolve by the aid of a gentle heat, and add to— 


Celloidin collodion (3 %) - 950 ccs, 
Then add— 

Citric acid . > ‘ 5 g. 

Warm alcohol ‘ ; : q.S. 


Enough alcohol should be used just to dissolve 
the acid. Shake thoroughly, and add :— 

16 g. 

20 ccs. 


Silver nitrate 
Hot water 


This should be added in small quantities at a 
time, shaking thoroughly between each addition. 
Allow the emulsion to stand for twenty-four 
hours, then filter and use. 


Hanneke’s Formula 

A. Celloidin collodion (4 %) . 620 ccs. 
Ether 2 : ; : 
Absolute alcohol - Se eae 

To this add— 

B. Silver nitrate. ‘ o> a ee 
Distilled water . : > bh ee. 
Absolute alcohol Re et Bae 


Then add in small quantities, shaking well after 
each addition and observing the order given :— 


C, Calcium chloride (crystal) 4 g. 
Distilled water 4 ccs. 
Absolute alcohol : 1 Ne 

D. Citric acid . . . 5 g. 
Distilled water . . 5 ccs 
Absolute alcohol : « BIOla 55 

EB. Castor oil . : ; oe es ae 
Glycerine . : : < ee 
Absolute alcoho ‘ STAR vy 


For solutions B, C, and D, the salts or acid 
should be dissolved in the water by the aid of 
heat and then the alcohol added; if this throws 
down any crystals the solution should be gently 
warmed, and as soon as clear added to the collo- 
dion. In all cases the solutions should be added 
in small quantities at a time with constant 
shaking in between, so as to obtain as fine- 
grained an emulsion as possible. 


Silver Bromide Printing-out Emulsion 


This was suggested in 1906 by Valenta, and 
gives an excellent printing-out paper. 


A. Celloidin collodion (3 %) . T,000° cea, 
B. Citric acid . : ! . 20 g. 
Absolute alcohol ‘ ‘ go ccs, 
Strontium bromide . 3 ae 
Glycerine . ? mn - 4 ccs, 
C. Silver nitrate : 20 g. 
Hot distilled water . sn AO, CCR. 
Absolute alcohol , o) Sas 
D. Ether. : 00 LES 


” 


Mix A and B in daylight and add C in the dark- 
room in small quantities with thorough agita- 
tion; add D, allow the emulsion to stand fiiteen 
minutes, and then filter through wool and use 
for coating. This gives an extremely rapid 


Collodion Emulsion 


printing paper with a long scale of gradation, 
and therefore requires rather brilliant negatives. 
An emulsion which is much more suitable for 
the average negative can be prepared by adding 
to the B solution :— 


Calcium chloride (anhydrous) O°5 g. 


Greater contrasts still can be obtained by using 
uranyl chloride or adding calcium chromate. 


Collodio-chloride Emulsion for Development 

This gives very slow plates, but the grain is 
exceptionally fine and very warm tones are 
obtainable. 


Magnesium chloride (crystal) . 4 g. 

Absolute alcohol . ; P2420, COM. 
Rub up in a mortar, and add— 

Collodion (2 %) 50 ccs, 


As soon as the mixture becomes slimy, add— 


Ether . . : ‘ «e530. ces. 
And finally add— 
Nitro-hydrochloric acid . 0-6 ccs. 


The silver collodion is prepared as follows :— 


Silver nitrate , P : 4 g. 

Hot distilled water F ; 2.009. 
When dissolved, add— 

Hot alcohol . F < 20 ccs, 
And then— 

Raw collodion (2 %) ‘. Snape CCF. 


The chloride collodion should be added to the 
silver collodion in small quantities, well shaken, 
and allowed to stand for twenty-four hours with 
occasional agitation; then it should be poured 
in a fine stream into about sixteen times its 
volume of warm water (100° F., or nearly 38° C.) 
with constant stirring. The emulsion is pre- 
cipitated in fine flocks, which should be collected 
on a clean linen filter, gently squeezed, and then 
well stirred up with warm water two or three 
times and finally well drained, rinsing once 
or twice with alcohol. Five parts of the dried 
emulsion should be dissolved in 100 parts of a 
mixture of equal volumes of alcohol and ether, 
shaken till dissolved, and then filtered. 

Pure bromide and chloro-bromide collodion 
emulsions were much used for transparency 
making, but of recent years the gelatine lantern 
plates have completely ousted them from prac- 
tical use. They are, however, now employed for 
negative work, and the most satisfactory formule 
are those given by Von Hiibl. 


Collodio-bramide Emulsion 
Silver nitrate 
Distilled water 


Dissolve, and add liq. ammonize (-880) in sufficient 
quantity to form a perfectly clear solution ; 
allow to cool, and add the silver solution to— 


Collodion (4 %) . - 600 ccs. 


This should be in a large bottle, preferably 
one that will contain about three times the total 
volume, and if any of the cotton or silver settles 


50 g. 
50 ccs. 


* oop 


119 


Collodion Filter 


out no notice need be taken of it. To this silver 
collodion add the following, whilst still warm :— 


Ammonium bromide 32 g. 
Hot distilled water 35. ccs. 
Alcohol ; : ‘ pangOe yy 


Shake the emulsion for about five minutes, and 
then add in small quantities with vigorous agita- 
tion about one-fourth of its volume of dis- 
tilled water. This causes the emulsion to pre- 
cipitate. It should then be poured into about 
ten times its bulk of water and well stirred, the 
water drained off, and the washing repeated 
three or four times. The shreds of emulsion are 
finally collected on a linen filter, and gently 
ptessed ; then shaken up with alcohol, and again 
pressed out. The emulsion shreds should now 
be shaken up with 8? oz. or 250 ccs. of absolute 
alcohol, and allowed to stand for twenty-four 
hours; at the end of this time 5} oz. or 150 ccs. 
of the liquid should be poured off and replaced 
by 54 oz or 150 ccs. of absolute alcohol in which 
74 grs. or o'5 g. of narcotine have been dis- 
solved, and 8$ oz. or 250 ccs. of ether added, well 
shaken, and allowed to stand three days and 
then— 


Absolute alcohol . i as 
Ether . ; ; 
added and the emulsion filtered. 
Chloro-bromide Emulsion 

This can be made in precisely the same way 
as described above by reducing the ammonium 
bromide to 416 grs. or 27 g. and adding 23 grs. 
or 1°§ g. of pure anhydrous lithium chloride. 
Both these emulsions are very suitable for posi- 
tive work and also for sensitising with eosine 
and other dyes for colour negatives. 

Von Hiibl recommends a glycin developer, but 
hydroquinone is the general favourite. Collodion 
positives and negatives can be intensified, re- 
duced, or toned like any other silver images. 

In process work, collodion emulsion has been 
revived of late years because of its suitability 
for colour work, owing to the emulsion being 
susceptible to colour sensitising with aniline 
dyes. <A chloro-bromide emulsion is used for 
this purpose, and it is always exposed in the 
moist state. ‘The sensitising dyes are sometimes 
added to the emulsion, and in other cases flowed 
over. Excellent emulsions are on the market, 


COLLODION, ENAMEL 

A mixture used for giving to prints the 
highest possible gloss, the process being called 
enamelling, an expression sometimes incor- 
rectly applied to burnishing and rubbing with 
encaustic paste. Enamel collodion may be 
purchased ready for use, or may be made accord- 
ing to the following formula :— 


250 ccs. 
250 » 


Pyroxyline . . aig? ets, 
Methylated alcoho 4 oz. 
Methylated ether : Ae aan 
Castor oil ‘ . 4 drops 


(For methods of using, see ‘‘ Enamelling Prints.”’) 


COLLODION FILTER (Fr., Filtre @ Collo- 
dion ; Ger., Kollodiumfiltrierfiasche) 

An arrangement for filtering the collodion 

used in the wet-plate process. As here shown, 


Collodion Pellicle 


a tuft of cotton is adjusted loosely in the lower 
part of the bulb-shaped receptacle at the top, 
the collodion being poured into this and filter- 
ing into the bottle beneath. A glass tube runs 


a 


Collodion Filter 


from top to bottom to allow of the escape of air 
as the filtered collodion ascends; this tube should 
be kept above the surface of the solution as the 
filtering proceeds. (See also “ Collodion Bottle.’’) 


COLLODION PELLICLE 

A pteparation, advertised and described by 
W. B. Bolton in 1876, for making sensitive 
plates which could be used in a dry or wet state, 


COLLODION POSITIVE 

A collodion negative image taken on thin, 
black-surfaced metal or on glass backed with 
velvet or black varnish. By reflected light the 
image appears as a positive. Collodion positives 
are usually made by the wet-plate process (see 
“* Collodion Process (Wet)’’). A thin image being 
necessary, the collodion should be diluted and 
development stopped directly the details are out. 
An iron developer gives the whitest deposit, and 
allows a shorter exposure to be given. Except 
when taken with a reversing mirror or prism in 
front of the lens, the ferrotype image is laterally 
reversed—that is, the left hand of the sitter 
appears as the right hand in the picture. The 
following developer gives an exceptionally white 
deposit suitable for ferrotypes, etc. :— 


Potassium nitrate . 200 grs. 22°8 g 
Ferric protosulphate . 300 ,, ye ae 
Acetic acid (glacial) . 14 0z 75 ccs 
Nitric acid (pure) . 30 mins, . eae 
Water 4 : « 20°02, T5000... 


Collodion positives must be varnished or 
glazed, as otherwise the film is abraded by hand- 
ling. 


COLLODION PROCESS (DRY) 

In this process plates and papers coated with 
a collodion emulsion (which see) are employed, 
thus obviating the great disadvantage of the older 
wet process in which the plates had to be exposed 
immediately they came from the sensitiser. Full 
information on preparing the emulsion ig given 
under the heading to which allusion is made 
above. Generally, collodion plates are of about 
the same speed as lantern plates, and they can 
be developed with any standard solutions used 
for gelatine dry plates, Glycine is particularly 
recommended owing to its freedom from fog. 


I20 


Collodion Process (Wet) 


COLLODION PROCESS (WET), OR WET- 
PLATE PROCESS (Fr., Procédé @ la col- 
lodion humide, Collodion mouillé; Ger., 
Kollodiumverfahven, Nasses kollodionver- 
fahren) 

Collodion was introduced into England in 
1847; immediately afterwards R. J. Bingham 
(one of Faraday’s assistants) suggested its use 
for photography. Gustave Le Gray, a noted 
French worker, also suggested that collodion 
might prove useful. The actual invention of the 
first workable process is due, however, to F. 
Scott Archer, who made the first collodion nega- 
tives in the autumn of 1848, and who published 
his perfected process in the Chemist for March, 
1851. So popular did Archer’s process become 
that it practically displaced daguerreotype and 
calotype, and it was almost exclusively used 
between 1855 to 1881. It is largely used to-day 
by process workers and by itinerant photo- 
graphers; while for certain other branches of 
photography—lantern slides, for example—it is 
considered by many to be unsurpassed. Its 
chief advantages are a structureless film, an ex- 
tremely fine grain, and clear whites. The fixing 
agent is easily washed out of the film, and the 
negative can be dried by heat. Wet-plate nega- 
tives can also be easily reduced and intensified. 

Wet plates are of low sensitiveness, their speed 
being about the same as_that of lantern plates. 

The photographer must prepare his own plates. 
A deep porcelain dish for the silver bath, a 
size larger than the plate to be sensitised, is 
required ; it must be scrupulously clean, and if it 
has previously contained other chemicals it must 
be very thoroughly washed. Place 480 grs. of 
silver nitrate in a clean pint bottle, and add 1 5 Oz. 
of distilled water (rain or tap water will not do). 
Shake until dissolved, and add 3 drops of pure 
nitric acid. Keep a day or two before using, 

Each ounce of the silver bath contains 32 grs. 
of silver nitrate, and the strength should be 
kept as near this as possible, using, if necessary, 
an argentometer for testing the density. The 
silver bath is filtered, poured into the porcelain 
dish, covered with a piece of cardboard, and 
placed in the corner of the dark-room that is 
farthest from the developing sink. Adjust the 
dark-room lamp so that a good light is thrown 
on the dish. Wet plates will stand far more red 
or yellow light than dry plates. 

For coating the glass the following are neces- 
sary :—(a) A 4-oz. bottle of Mawson’s collodion, 
with iodiser in a separate bottle. Before use the 
iodiser is poured into the collodion, and this 
iodised collodion will keep in good condition for 
several months, becoming deep red in colour, the 
plates then requiring a much longer exposure, 
Iodised collodion can be purchased teady for 
use, but the plan here described is preferable. 
(6) Rubber solution for edging the plate. 

For developing, fixing, etc., obtain :— 
Pyrogallic acid : . - 1.0%, 
Glacial acetic acid E Ms 
Ferric protosulphate ° Ib. 
Mercuric bichloride . Oz, 
Liquor ammonie . . 

Lead nitrate : 

Potassium ferricyanide ; 

Sodium hyposulphite or potas- 

sium cyanide . . ° 


e e e ° . 


St ee Oe 


x 


y* 
3 


Collodion Process (Wet) 


Before coating with collodion, the plate is 
““edged’’ to prevent the film from leaving the 
glass. A drop of rubber solution is taken up 
on a piece of cotton-wool and run round the edge 
of the glass, and the plate is then ready for 
coating. 

Take the glass at one corner between the finger 
and thumb, and pour a small pool of collodion 
upon it. Carefully tilt the glass so that the 
collodion flows to the corner farthest from the 
fingers, tilt again into the other top corner, 
next bring the collodion to the corner nearest 
the thumb, and then pour the surplus back into 
the bottle via the remaining corner. While 
the collodion is being poured into the bottle the 
plate must be kept moving to and fro laterally, 
or the cellodion will set in ribs. This movement 
of the plate must be continued for several seconds, 
till the collodion is set. Replace the stopper 
in the collodion bottle, close the door of the 
dark-room, and immerse the plate in the sensitis- 
ing solution, 

When placing the plate in the silver bath, the 
dish should be tilted, so that the solution flows 
to one end. Place the plate in the other end of 
the dish, and immediately lower the dish to let 
the bath flow in an even wave over the plate. If 
the flow is checked, a streak across the image 
will result on development. The cover of the 
dish is now replaced, and the door of the dark- 
room can be opened for a minute or so. 

Sensitising begins directly the plate is inserted 
in the bath, and is complete in about two and a 
half minutes. The plate is ready to be removed 
from the bath when the film presents a creamy 
appearance; but, as a rule, leaving the plate in 
the bath for two or three minutes will suffice. 
Of course, if it is desired to look at the plate 
while in the bath the door of the dark-room must 
be closed. 

If ordinary dry-plate slides are to be used the 
rebates for the glass must first be covered with 
strips of blotting-paper. If the wet plate 
touches the woodwork of the slide, scum will 
form over the plate and the picture will be 
spoilt. If the strips of blotting-paper are damped 
before use they can easily be fixed in the rebate. 
Wet-plate slides are provided with silver wires 
with the object of supporting the plate, but even 
these slides require blotting-paper at the bottom 
and top of the plate. After remaining in the bath 
for two or three minutes the plate is removed by 
being raised with the handle of a silver spoon, 
or with a lifter made of horn or vulcanite. The 
fingers must not be dipped into the silver bath, 
and neither wood nor metal, other than silver, 
must be used. The collodion of the sensitised 
plate has a creamy, opalescent appearance, 
owing to the formation of silver iodide in the 
film 


The plate is allowed to drain for a few seconds 
over the bath, and the moisture is then removed 
from the back with a piece of blotting-paper, 
the plate meanwhile resting on its edge upon >a 
sheet of clean paper. 

Next, the plate is inserted in the dark-slide, 
care being taken that the collodion film is not 
in contact with either wood or metal. The expo- 
sure for wet plates is from ten to twenty times 
longer than is required for an ordinary dry plate ; 
fresh collodion requires less exposure than stale, 


I21 


Collodion Process (Wet) 


and in cold weather the sensitiveness of the film 
is considerably diminished. In a weak light or 
in a slightly yellow one a wet collodion plate 
is far less effective than a gelatine film. 

_ An acid, instead of an alkaline, developer 
is necessary for wet collodion plates. ‘The fol- 
lowing is a formula for a pyro developer stock 
solution :— 


Pyrogallic acid 


. 24 grs. 
Glacial acetic acid 


2 OZ. 


This solution keeps well. For use, add 6 parts 
of water to 1 part of the stock solution. 

The above is quite reliable, but some workers 
prefer ferric sulphate, as in the following :— 


Ferric protosulphate 1 02. 
Glacial acetic acid ; tae a" 
Water ee BG 


Methylated spirit should be added to the 
developer after the bath has been in use some 
time, to ensure even flowing of the solution over 
the plate. A shorter exposure is required for iron 
development. Developing and fixing dishes are 
not required. The plate is removed from the 
dark-slide, and the developer is poured quickly 
and evenly over the film. The plate is kept mov- 
ing during development, in order to keep the 
film covered with solution. Fresh developer 
must be used for each plate. The image develops 
steadily, and usually begins to appear in about 
ten seconds; but in cold weather the time may 
be considerably longer. Development is stopped 
when all the details are visible. The plate is 
washed for a few seconds under the tap and is 
then fixed with potassium cyanide, which should 
be kept in a saturated solution, and for use diluted 
with double its volume of water. 

“Hypo ”’ can be used instead of cyanide; but 
it does not work so quickly, and takes longer to 
wash out of the film. After fixing with potassium 
cyanide, the plate is washed for a minute or so 
under the tap; if “hypo” is the fixing agent, 
five minutes’ washing is necessary. If the pic- 
ture is satisfactory, the plate can be dried in 
front of the fire. The collodion image, when 
fixed, should be bright and clear, without a trace 
of fog or stain. The best reducer, should one be 
found necessary, is cyanide and iodine, made by 
dissolving a few crystals of iodine in methylated 
spirit and adding a saturated solution of potas- 
sium cyanide until the red colour of the iodine 
has disappeared. 

If intensification is required, a solution of 
mercuric bichloride, followed by ammonia, can 
be used as in dry plate operations. If the image 
is very flat, or when black-and-white work is re- 
quired, intensification with lead nitrate can be 
adopted, using :— 


Lead nitrate . ‘ pee. 
Potassium ferricyanide . one ere 
Water : ¢10--O2; 


The plate is immersed in the above solution 
till sufficient density is reached, then washed 
under the tap till all yellowness has disappeared. 
The picture, in most cases, need not be blackened 
when intensified by lead, as sufficient density 
is obtained without the use of an alkali. When 
absolute opacity is required, ammonium hydro- 
sulphuret can be used, after all the yellow stain 


Collodion Transfers 122 


has been washed from the film. It must be 
noted that the lead intensifier has a drastic 
action and must be used only for flat pictures 
or for the reproduction of black-and-white draw- 
ings. 

Another method of intensification, known as 
re-development, is perhaps the best for beginners, 
When the image, after fixing, seems to be lack- 
ing in contrast, the plate is rinsed and fresh 
developer, mixed with a few drops of a 10 per 
cent. solution of silver nitrate, is flowed over the 
film. The addition of the silver to the developer 
gives vigour to the image, After fixing the plate, 
mercuric intensification will give further con- 
trast, if necessary. When dry, the plate should 
be varnished, as the collodion film is easily torn, 

For ferrotype plates, a thinner film is neces- 
sary, and the iodised collodion should be further 
diluted with sulphuric ether, A developer giving 
a white deposit (see ‘‘Collodion Positive ) 
should be used. The general procedure of sen- 
sitising, developing, and fixing ferrotypes is the 
same as for wet-plate negatives. 

In process work, a very clean working collodion 
is required, and at the same time one that gives 
great density. Further, the film must be tough 
to withstand intensification and _ reduction. 
Celloidin collodion of not more than 2 per cent. 
Strength is usually employed. Pure solvents 
have to be used in order to avoid fog and scum. 
Ammonium and cadmium iodide and cadmium 
bromide with cadmium chloride are the general 
ingredients of the iodiser. A typical formula 
for collodion suitable for process work is— 


Celloidin . : . T*O2, kh tak 2 
Alcohol (805) . «| 40 5,0 “5996 "ces: 
Ether (-720) ; a OO" 5) nd FOd te 
The following is the iodiser :— 
Alcohol (-820) IO Oz. 284 ccs. 
Cadmium iodide P reer aay Ss 
Ammonium iodide 180 grs, 116 ,; 
Cadmium bromide ARG 1 aieee Tike 
Cadmium chloride alge 8 SY 3 
Iodine ; ‘ Fe LOTS “is 


Take one part iodiser to nine parts collodion, 
and allow to stand for ten to fourteen days. 
The silver bath is usually 35 to 4o gers. per oz. 
Development is with the iron developer ; fixing 
with potassium cyanide; intensification with 
either lead nitrate (for line negatives), or with 
copper bromide (for half-tone), followed with 
ammonium or sodium sulphide. “ Cutting” or 
reducing to sharpen up the dots or lines is gener- 
ally resorted to, the solutions employed being 
iodine and cyanide. For stripping, the negatives 
are coated with rubber solution and then with 
collodion to which a small proportion of castor 
oil has been added to make it flexible, The glass 
plates are, as a rule, edged with rubber solution 
before coating with collodion, to make the latter 
hold. 


COLLODION TRANSFERS 

Collodion positives transferred from the ori- 
ginal glass to other supports, usually paper. 
Special collodions and papers for transfer work 
are now commercial articles, and the process is 
quite easy nowadays, compared with what it was 
in 1857, when it was first practised no special 


Colloids 


collodions for the purpose being then obtain- 
able. A suitable transfer paper is made by evenly 
coating smooth-surfaced cream-wove foolscap 
with a solution of gelatine made by dissolving 
% oz. of gelatine in from 20 to 30 oz, of water, 
and then drying. After the collodion picture is 
fixed and washed in the usual way, the transfer 
paper is soaked and carefully squeegeed into con- 
tact with the picture, film to film, and allowed 
to dry. When dry, one corner of the paper may 
be lifted with a penknife, when it will strip 
from the glass and bring the picture with it, If 
the pictures to be transferred are large, the 
glass should be coated with a substratum of wax 
before the usual collodion is applied. Five grains 
of pure sun-bleached white wax in 1 oz. of ether 
forms the waxing solution ; this is spread evenly 
and rapidly over the glass, and, when dry, polished 
until no trace of the wax apparently remains, 
although enough will be left to assist the picture 
to leave the glass easily. In some cases, negative 
films, too much under-exposed to print from, 
were bleached by means of mercury and trans- 
ferred to black paper, on which they appeared to 
be positive and finished pictures. 


COLLODIONISED PAPER 


A term somewhat loosely applied to collodio- 
chloride paper. 


COLLODIOTYPE 


An eatly name for any kind of photograph 
produced by the collodion process. 


COLLOGRAPHIC PROCESSES 

A general term applied to collotype methods, 
all based on the principle of the action of light 
on a bichromated colloid, the latter being 
usually gelatine. 


COLLOGRAPHY 

A process said to have been invented by 
Pumphrey, of Birmingham, in 1880, and similar 
to that formerly well known under such terms. 
as “ Autocopyist,” etc., in which a film of 
gelatine on glass or on some flexible support, 
such as parchment, was bichromatised and 
dried. Writing or drawing is done on a suit- 
able paper with solutions of iron salts, nutgalls, 
ot similar substances having a tanning action 
on the gelatine surface, to which the design is 
next transferred. By keeping the gelatine pad 
moist and applying an ink roller, the lines will 
take the greasy ink, but the white parts wili 
repel it. Paper is then brought into contact 
with the pad, and an impression taken by 
rubbing or squeegeeing. 


COLLOGRAVURE 

A kind of collotype invented by Balagny, of 
Paris, in 1893-4, in which gelatino -bromide of 
silver films were converted into collotype printing 
sutfaces, the prints being made with fatty ink. 


COLLOIDS 


A name derived from Greek holla (glue) and 
erdos (appearance), and given by Graham to 
those non-crystalline substances which do not 
diffuse through porous membranes. ‘The chief 
organic colloids are cellulose, starch, dextrine, 
tannin, gelatine, caramel, and albumen. The 


Colloids 


inorganic colloids are hydrated oxides of iron, 
hydrated silica, alumina, etc. 

Grahatin, in 1861, discovered that many sub- 
stances, particularly those which readily crystal- 
lise, diffuse through animal membranes, whilst 
other substances, such as gelatine, which do not 
crystallise, do not so diffuse. (Modern researches 
have shown that Graham’s conclusions must be 
modified somewhat.) The latter class of bodies 
he called “‘ colloids.” The diffusion of the crystal- 

-line salts through a membrane he termed 

** dialysis,’ and the vessel in which the solution 
was placed a “dialyser.” There are a great 
many natural or organic substances, such as 
starch, dextrine, gums, albumen, caramel, rubber, 
resin, etc., which are colloids and behave pre- 
cisely in the same way as the first-mentioned 
gelatine; but there are also many inorganic 
chemicals, such as ferric hydrate, silicic acid, 
etc., which act similarly. Apparently these 
dissolve in water, but when submitted to the 
test of dialysis prove themselves to be true 
colloids. The apparent solutions of such sub- 
stances are called “‘ pseudo-solutions,” to differ- 
entiate them from the so-called true solutions. 

Graham also discovered that water was not 
unique in forming colloidal solutions, but that 
alcohol, benzole, glycerine, and sulphuric acid, 
as well as other solvents, were capable of acting 
in the same way; and the term “sol”’ is used to 
designate these. Thus, hydrosol indicates a 
water sol, alkosol an alcoholic sol, and glycerosol 
a glycerine colloidal sol. Generally, when the 
solution is of an organic nature, it is termed an 
“‘ organosol,”’ 

The scientific student may here be told that, 
practically, a sol or colloidal solution consists 
of two ingredients, a liquid and a solid, the latter 
being in an extremely finely divided state, dis- 
tributed or suspended in the liquid. The 
sharply separated parts of the sol are said to 
be its phases, and in colloidal solutions there are 
several multiple-phase or heterogeneous forma- 
tions, and the one phase, being in an extremely 
finely divided state, naturally presents to the 
second phase a very large surface, and with 
normal examination the sol appear perfectly 
homogeneous. This is called ‘‘ microhetero- 
geneity.” Many substances, particularly those 
which form jellies or “‘ gels,’’ do not, however, 
show this particular form of heterogeneity, par- 
ticularly when coagulation is effected, and then 
it is termed ‘“‘ macroheterogeneity.’’ In con- 
tinental literature, the term “ disperse-hetero- 
gene ’’ is used for the former, and a generic term 
of “dispersoids”’ is used for all microhetero- 
geneous systems. Other colloid solutions take 
another form, and this has been likened to a 
sponge, that is, they practically form a network 
distributed throughout the dispersion medium. 

The density of colloidal solutions cannot be 
calculated from the densities of the disperse 
phase and the dispersion medium, or the sub- 
stance and solvent; for instance, a solution of a 
given quantity of gelatine in a given quantity of 
water is not the sum of their respective volumes, 
but less, a small but marked contraction taking 
place. Their osmotic pressure is very low, and 
in many cases not to be detected, and their 
boiling and freezing points vary but very slightly 
from those of the liquid, water, alcohol, etc. 


123 Colloids 


It has been already stated that colloids would 
not diffuse through an animal membrane, but 
recent researches have shown that this is only 
partially true, and that some colloids will diffuse 
as well as crystalloids, but at a much slower 
tate, so that the fundamental difference is in 
their rate of diffusion. 

Provided that the size of the particles of the 
disperse phase are sufficiently small, they exhibit 
under a powerful microscope peculiar vibratory 
motions, which were first discovered by Brown 
in 1827, and are therefore called ‘‘ Brownian 
movements,” This motion is approximately a 
zig-zag or to-and-fro motion, and has been 
ascribed to the contrary pull of gravity and the 
viscosity or thickness of the liquid. Particles 
which are larger than 3 to 5 4 (1 « = ‘oor milli- 
metre = 5557 in.) do not show this movement. 
Many hydrosols appear perfectly clear and homo- 
geneous, but others exhibit the phenomena of 
fluorescence or opalescence when illuminated by 
suitable light, and Tyndall’s phenomenon is often 
apparent with light of very small wave length, 
that is to say, the particles are sufficiently large 
to reflect violet or ultra-violet light of extremely 
short wave length, and polarise it. This is the 
foundation of ultramicroscopy. 

The disperse phase carries a positive or nega- 
tive electric charge, which is dependent to some 
extent on the dispersion medium—that is, the 
water or other liquid—and sometimes on its 
alkalinity or acidity. Colloidal solutions can 
exhibit a change of condition under mechanical 
action, or the application of heat, and the dis- 
solved substance may separate in an insoluble 
form or be converted into jellies by the addition 
or certain substances, such as electrolytes. When 
the substance separates out in an insoluble form 
it is known as a “ gel,’’? and if formed from an 
aqueous solution it is known as a “ hydrogel,” 
an “‘alkogel’”’ from alcohol, and a “ sulfogel”’ 
from sulphuric acid, etc. The process of the 
formation of the gel is called pectinisation or 
coagulation. When the residue left after coagu- 
lation’is soluble in water, the process is said to 
be reversible; if insoluble, it is irreversible. 
Frequently an insoluble and otherwise irrevers- 
ible colloid is precipitated in the presence of a 
reversible colloid; it also becomes reversible; 
and the colloid that produces this state is known 
as a protective colloid, or, to use the German 
word, a “‘schutz-kolloide.’’ Lottermoser has also 
pointed out that by certain precipitating agents 
a colloid may be precipitated from the hydrosol 
in such a condition that it will again form a 
hydrosol, and therefore suggests the terms 
“solid”? and ‘“‘liquid’’ hydrosol, and confines 
the term hydrogel to the insoluble amorphous 
substance. The law is that sols with opposite 
electric charge precipitate one another, but 
those of like charge do not. 

Gels or jellies may be considered as colloid 
solutions in which the disperse phase is in a 
higher concentration, and molecular and col- 
loidal solutions can diffuse through a gel more 
or less rapidly, according to the concentration 
of the disperse phase of the gel. 

Colloidal solutions differ from true solutions 
in that the latter are perfectly homogeneous 
under the most critical visual examination that 
can be applied, whilst the former show the 


Collotype 


particles under sufficiently high power as already 
pointed out. They differ also from suspension 
liquids or mixtures in that in the latter the 
particles or disperse phase are sufficiently large 
to be seen with the naked eye or a weak power. 
There is, however, some evidence to prove that 
these divisions are but arbitrary, and that so- 
called true solutions may be of a colloid nature. 

P, Weimarn and Wolfgang Ostwald (“ Grun- 
driss der Kolloidchemie”’ ) considering that, as sus- 
pensions, colloidal and true solutions are merely 
varying degrees of dispersion, have proposed, 
the name of “ dispersoids,’ and the latter 
divides them into (1) coarse dispersions, such as 
Suspensions and emulsions; (2) colloidal solu- 
tions; (3) molecular dispersoids; and (4) ion- 
dispersoids, assuming that free ions exist. The 
crystalloid solutions belong to classes (3) and (4). 
The above classes merge one into the other, and 
colloidal solutions are divided into suspension 
colloids and emulsion colloids, which are also 
termed suspensoids and emulsoids. The occur- 
tence of colloidal silver and gold is assumed 
in many photographic processes, and many 
reactions can only be satisfactorily explained on 
this assumption. There is, however, an increas- 
ing tendency to drag the phenomena of colloids 
into every obscure photographic process, and 
there is the grave danger that it may be used 
merely to cloak our ignorance of the true state 
of affairs. 


COLLOTYPE 
druck) 

A process known also as “ phototype,” and, 
in slight variations, as ‘“‘ Albertype,” “ Arto- 
type,” etc. It is based on the principle that 
if a film of bichromated gelatine is exposed 
to light under a negative, and the unaltered 
bichromate is washed out, the film will have a 
similar property to that possessed by a litho- 
graphic stone of attracting ink in some parts 
and absorbing water in others, the water repelling 
the ink. It differs essentially, however, from 
lithographic work in the fact that the attraction 
for ink and water in the different parts is pro- 
portionate to the action of the light, so that 
the strength of the ink image varies in proportion 
to the light and shade of the picture. The dis- 
covery of this property was made by Fox 
Talbot in 1853, and his researches were followed 
up by A. Poitevin, of Paris, from 1856 onward. 
The first practical collotype process was intro- 
duced by ‘Tessié du Motay and Ch. R. 
Maréchal, of Metz, in 1865; and the perfection 
of the present-day process of collotype is due 
to the labours of Josef Albert, Husnik, and 
Obernetter, Although the process is still largely 
worked, its commercial success has been much 
retarded of late years by the progress of half- 
tone, photogravure, and other etching methods, 
and it has to a considerable extent fallen into 
disfavour, especially in England and America. 

The general method of working the process 
is as follows :—A thick glass plate is ground on 
one side with fine emery powder, and is then 
placed on a levelling stand or levelling screws, 
and having first been coated with a suitable 
substratum and dried, is flowed over with a 
measured quantity of bichromated gelatine. 
When the film is set the plate is placed in a dry- 


(Fr., Phototypie ; Ger., Licht- 


124 


Colour 


ing oven, which is brought up to a temperature 
not higher than 130° F. (54° C.), at which the dry- 
ing takes about two hours. When cool, the plate 
is placed with the negative in a special printing 
frame, pressure being applied by wedges. The 
plate is next washed to remove the unaltered 
bichromate, and allowed to dry. To prepare the 
image for printing, the surface is fooded with a 
mixture of glycerine, water, and sometimes other 
ingredients, allowing it to stand for thirty minutes. 
Then the excess is removed and the plate is 
rolled up with a lithographic roller charged 
with a special collotype ink, which is similar 
to lithographic ink, but stiffer, When com- 
pletely inked, paper is laid on the plate and 
pressure applied in a press. An ink image re- 
producing the tones of the original is thus 
obtained. Success depends on the proper form- 
ation of a grain caused by reticulation of the 
gelatine during the drying, and the grain is 
modified by exposure according to the action of 
the light passing through different parts of the 
negative, 

Many ‘modifications of detail have been made 
by different workers, but the above general out- 
line applies to all the methods, except that in 
Some cases attempts have been made to form 
the image on aluminium, copper, lead, and other 
plates instead of glass. 

Collotype in colours has been worked with 
success for some years in Germany, and to some 
extent in England. The number of negatives 
made varies with the number of different colours 
required. A collotype plate is made from each 
negative, and all its parts are blocked out except 
those required for that particular colour. The 
printing is then done as in chromo-lithography, 
the impressions of each colour being super- 
imposed in exact register. 


COLOPHONY 
phonium) 
Another name for resin, more used on the 
Continent than in England. Properly it is 
applied to a black resin, the solid residuum of 
the distillation of turpentine after the oil has 
been worked off. (Particulars of resins are given 
under the heading “‘Gums and Resins.’’) 


COLORIMETER (Fr., Colorimétre ; Ger., Far- 
benmesser) 

An instrument for ascertaining the strength 
or putity of a substance by comparing its colour 
with a given standard. There are several forms, 
as, for example, Mill’s, in which the colour is 
varied by altering the depth of a tinted solution 
until a match is obtained ; Lovibond’s, in which 
a number of coloured glasses are adjusted; and 
so on. A colorimeter is occasionally useful in 
photography, as, for instance, in the volu- 
metric estimation of silver nitrate solution with 
potassium chromate, in which it is often difficult 
to recognise the red reaction that ensues owing 
to the original yellow colour of the test solution 
itself. A properly adjusted colorimeter renders 
the change of tint at once manifest. 


COLOUR (Fr., Couleur ; Ger., Farbe) 

A person sitting in a perfectly dark room can 
see neither the form nor colour of the objects 
around him; but the moment light is admitted 


(Fr., Colophane; Ger., Colo- 


i 


Colour 125 Colour 


TABLE OF SUBTRACTIVE COLOUR MIXTURES OR SUBTRACTIVE ANALYSIS (STOLZE) 


Orange Yellow ine Green Blue green ee - ee 
| Indigo blue 
Blue Cyan. blue 
Greenish | Greenish Bluish Blue green 
blue blue grey 
Bluish Blue Blue Grey Green 
green green green 
Yellowish Green Bluish Green Violet Yellow 
green green grey green 
Greenish Yellow- Yellow Green Yellowish | Dirty red | Yellow 
yellow green | green olive brown 
Gold Olive Yellowish Yellowish Olive Olive Red- Orange 
yellow grey grey grey brown 
Deep red | Yellowish | Greyish | Yellowish Grey Grey Greyish | Dirty red | Deep red 
red yellow grey violet brown violet 
Deep red | Scarlet | Yellowish Grey Bluish Bluish Violet Red Purple 
grey grey violet violet 


he at once sees the shape of objects and also seen in their original purity and strength, whereas 
their colours. It is obvious then that to have in the case of the grey surface, the colours are 
colour there must be light. Colour is due to _ still there, but they are reduced in luminosity, 
the suppression or absorption of some of the that is, they appear less brilliant. With a black 
constituent rays of white light (see “‘Spec- surface, such as good black velvet, the colours 
trum’’). A sheet of red glass looks red because are absorbed entirely. 

it has suppressed or absorbed that particular Colour may also be formed by the interfer- 
region of the spectrum or those colours to which ence of the light rays with one another, but this 
ted is complementary (see “Colour, Comple- is also a suppression of some of the spectral 
mentary ’’), and itis the residuary colours that rays. (See “‘ Interference of Light.’’) 

give the observer the impression of red. Pre- It is usual, therefore, to designate colours as 
cisely the same thing happens with any substance ‘“‘ body colours” and ‘“‘surface or interference 
which is not transparent, as, for instance, a  colours.’’ To the former class belong all coloured 
sheet of red paper or a green leaf; the light pigments, and to the latter those colours seen 
incident on its surface penetrates to a slight on a diffraction grating, a thin soap bubble or a 
depth into the substance of the paper or leaf, peacock’s tail feathers. 

and there meets with a material or surface which It is important to differentiate between the 
reflects the light back to the eye, but in its action of mixed pigments and mixed lights, as 
passage into and out of the paper or leaf the the results are not comparable. In the former 
light undergoes selective absorption, and the case, mixing increases in each case the suppres- 
residuum of the incident light now appears’ sion or absorption of light with each pigment 
either red or green. used, whereas the mixing of coloured lights adds 


White, grey, and black are not colours; the light to light. To illustrate the first point, take 


first is the sum of all the spectral rays; grey is three printing inks, red, yellow, and blue, such 
all the rays reduced in intensity ; whilst black as are used in trichromatic printing, and examine 
is the suppression of all light, and therefore of the absorption spectrum of each. The letters 
all colour. This can be strikingly illustrated by atthe top of the diagram refer to the Fraunhofer 
projecting a spectrum or a series of coloured lines, the colours being placed underneath ; the 
glasses or filters on to a white, agrey, andablack black portions show the assumed absorptions 
surface. In the first case, all the colours are of the inks, whilst the white portions show the 


TABLE OF ADDITIVE COLOUR MIXTURES OR OPTICAL SYNTHESIS (HELMHOLTZ) 


Violet Indigo blue | Cyan. blue Blue green ee Yellow 
Red Purple Dark Whitish White Whitish Golden Orange 
crimson crimson * yellow yellow 
Orange Dark Whitish White Whitish Yellow Yellow 
crimson crimson yellow 
Yellow Whitish White Whitish Whitish Greenish 
crimson green green yellow 
Greenish White Whitish Whitish Green 
yellow green green 
Green Whitish Water Blue green 
blue blue 


Blue green| Water blue | Water blue 
Cyan. blue | Indigo blue 


Colour Absorption 


light reflected, the sum of which is severally 
red, yellow, and blue. Now, it is obvious that 
by superimposing these three spectra there is 
no part which is transmitted by all three, and 
the result is total absorption of light, or black. 
Taking the case of three-coloured lights, by 
mixing them on a screen by means of a triple 
lantern, just the reverse of the above effect is 
obtained; for convenience, let there be taken 
red, yellow, and blue glasses, matching approxi- 
mately the inks referred to above. Then, con- 
sidering not the absorptions or black portions, 
but the white or transmitted portions in the 
figure, it will be understood that the whole 
spectrum is transmitted and the result is white 
light. 

The former is called subtractive colour mixing 
or analysis, whilst the latter is termed additive 
colour synthesis. It must not be overlooked 
that whilst pigmentary colours have been 
dealt with, in the case of subtractive colour 
analysis, the argument applies also to super- 
imposed transparent colour filters. 

The tables on the preceding page show the 
difference between the two systems. 


A. ° 8 Co 0 € Ea Set 


Yellow {nh 


Blue tak 


Green Blue 


Red Orange Yellow Violet 


Diagram Indicating Absorption Spectra of Red, 
Yellow and Blue Printing Inks 


In these tables the colour resulting from a 
mixture of any two colours is found where the 
vertical and horizontal colours meet. Also, the 
term “ whitish’ means that the colour appears 
pale—that is, mixed with white light. It is 
usual to designate the main or predominant 
colour and precede it by the colour with which 
it is mixed; for instance, there may be a full 
or pure green; when mixed with blue, this 
becomes bluish-green ; with still more blue, a 
pure blue-green; with increasing quantity of 
blue, it becomes greenish-blue. 


COLOUR ABSORPTION 

Whilst colour itself is an absorption of light 
(see “Colour’’), it is extremely important in 
some cases to know the colours absorbed by 
certain materials, such as aniline dyes for filter 
making. The only method of determining this 
satisfactorily is by means of a spectroscope, or, 
for accurate work, a spectro-photometer, It is 
laborious work, as the absorption of a dye solu- 
tion will alter with increased concentration or 
depth of solution, and it is necessary, therefore, 
to make very careful spectro-photometric obser- 
vations at various dilutions, This, however, can 


126 


Colour, Complementary 


be performed much more readily by photography, 
as has been done by Uhler and Wood, of the 
Carnegie University, of Washington, U.S.A., and 
more completely by Wratten and Wainwright in 
their “ Atlas of Absorption Spectra,” which con- 
tains the absorption spectra of 170 dyes. For 
this work was used a small box spectrograph 
fitted with a prism grating, and the dye solution 
was contained in a wedge cell of rectangular form 
of 1 cm. (-4 in.) internal length and 5 mm, 
internal width, with a diagonal partition which 
divided it into two wedge-shaped cells, the one 
being filled with the dye solution and the other 
with the solvent, so as to obviate the prismatic 
effect of the cell. The thickness of the dye 
solution thus varied considerably, the actual 
thickness from end to end of the slit being about 
I to 15. The spectrograph was provided with a 
wave length scale and an ultra-violet filter. Pre- 
cisely the same results can be obtained by using 
a parallel-sided cell of fixed width and varying 
the strength of the solution, or keeping the dye 
strength constant and varying the cell width, 
but these plans are laborious and do not give 
the required information in such compact form. 


COLOUR, COMPLEMENTARY (Fr., Couleur 
complémentaive; Ger., Komplementar- 
farben) ; 

For every saturated and unsaturated colour 
there exists another colour which, when suitably 
mixed with it, forms white ; such pairs are called 
complementary colours. It is important to 
know—roughly, at any rate—the complementary 
colours, because one can at once determine the 
colour of the filter required to absorb one or 
the other. For instance, supposing one had to 
photograph a photomicrographic object which 
was stained green and blue in parts, and it was 
desired clearly to differentiate the green; then 
all one would require to know would be the com- 
plementary colour to green, and a filter of that 
colour would absorb the green and show it as 
black. On the other hand, if one wanted to 
show the green and suppress the blue-stained 
portions, then one would only require to know 
the complementary colour to the blue to absorb 
this and render the green clear. 

The following table, compiled by Prof, Griin- 
berg, of Vienna, contains the sum of the observa- 
tions of the leading physicists of the day :— 


aa ar ee ee 


Wave Wave 

Colour length pai et length 

im Be coer im jy 
Red 656 Greenish blue 492 
Orange 608 ae 489 
585 ue 483 
Gold yellow ; 396 Blue ra 
571 ndigo blue 462 
Yellows 1566 | Indigo blue 447 
Greenish yellow; 564 Violet 433 


He also gives the following very simple 
formula for finding approximately the com- 
plementary colour :— 


5.59 
in which I’ = the complementary colour and 


Colour, Effect of 


L, the given wave length. Ex.—What is the 
complementary to wave length 589? 


I’ = 498 
2 
<4 = 498 — 14°13 = 483-87 
There is no true spectral colour complementary 
to the pure green spectrum region ; this is found 
in the purples or crimsons made by a mixture 
of violet and red. (See also “ Zander’s Comple- 

mentary Colour Process.’’) 


COLOUR, EFFECT OF 


The effect of the various colours on the photo- 
gtaphic emulsion is dependent chiefly on whether 
the emulsion is colour-sensitised or not, on the 
use of colour filters, and the length of the 
exposure. The ordinary (non-colour-sensitised) 
plate is sensitive to the ultra-violet, violet and 
blue rays, the commercial iso- or orthochromatic 
plate has an added sensitiveness to yellowish- 
green and yellow, whilst the panchromatic plate 
has red sensitiveness as well. 

There is one effect of colour which is particu- 
larly marked when using screenplates, and that 
is the effect of reflections from surrounding 
coloured objects on a sitter or object. When 
dealing with ordinary monochrome photography 
this is entirely overlooked, but with colour repro- 
ductions these coloured reflections obtrude them- 
selves sometimes in the most unexpected manner. 


COLOUR FILTER 
Filter.’’) 


COLOUR FOG (See “ Fog, Colour.’’) 


COLOUR, FUNDAMENTAL 
Sensations.’’) 


COLOUR PHOTOGRAPHY (See “‘ Auto- 
Curome. Process,” “Ives’ . Process,” 
“Tippman’s Process,”  ‘*Screenplate 
Colour Photography,” etc.) 


COLOUR, POSITIVES IN 
in Colours.’’) 


COLOUR SCREEN OR FILTER 


A sheet of coloured glass, or glass coated with 
dyed gelatine or collodion, or a cell containing 
a coloured liquid, used to modify the action of 
some particular region of the spectrum on the 
sensitive plate. It is usual to divide colour 
screens into two classes, (a) continuing and (d) 
contrast screens, though the division is purely 
arbitrary and the two insensibly merge one into 
the other. The most used form of screen or 
filter is the yellow screen, which is employed 
with iso- or orthochromatic plates to reduce 
the excessive action of the ultra-violet, the 
violet and blue rays, which it does by partially 
or wholly absorbing them, and thus, by prolong- 
ing the exposure, gives the green and yellow rays 
more time to act so that the colours may be 
reproduced more nearly in the order of their 
respective visual luminosities (see ‘‘ Colour 
Sensations” and ‘“‘ Luminosity, Visual’’). The 
exact depth of the yellow screen is dependent 
on the relative sensitiveness of the emulsion to 
the yellow and blue, and also on the effect desired. 
For instance, in photographing extremely faint 


(See “Colour Screen or 


(See “Colour 


(See ‘* Positives 


127 


Colour Screen 


white cirrus clouds against a blue sky the differ- 
ence in photo-chemical action of the sky and 
clouds is so slight that a contrast or deep-coloured 
screen is used abnormally to suppress the action 
of the sky. On the other hand, when it comes 
to a pictorial representation of a field of wheat 
intermingled with poppies, the visual lumin- 
osities of which may be approximately equal, 
the operator’s esthetic feeling or education must 
teach him to choose either to disregard the truth 
and to accentuate the golden hue of the wheat at 
the expense of the scarlet poppy, or else to obtain 
a compromise between the two. In such a case 
another factor, of the permissible exposure, comes 
into play. 

Numerous dyes have been used or suggested 
for making the yellow screen, which has now 
largely replaced the old form of pot glass orange- 
colour screen, which contained also a consider- 
able proportion of black that merely increased 
the exposure by cutting down the available 
light. Aurantia, auramine, naphthol yellow, 
methyl orange, tartrazine, and filter yellow K, 
have all been used. Of these, the last is by 
far the most effective, as it completely suppresses 
the ultra-violet rays, which are invisible to us, 
and has a gradual absorption for the violet and 
blue. It is a very soluble dye, and is stable to 
light in the ordinary way. 

The following instructions are modifications 
of those issued by the Hoechst Dyeworks, the 
makers of this dye, for the manufacture of yellow 
screens, and they may be considered typical for 
making all filters, the quantities and dyes merely 
varying according to the particular requirements, 


Stock Dye Solution 


Filter yellow K 31 grs. 2 g. 
Distilled water. 140z.38 mins. 400 ccs. 
Stock Gelatine Solution 

Gelatine (hard emul- 
sion) . : . 420 gts. 60 g. 
Distilled water to 16 oz. 1,000 ccs. 


Wash the gelatine by stirring two or three times 
in distilled water, then drain and add to about 
three-quarters of the total quantity of water, 
dissolve in a water bath at 120° F., and if it is 
to be kept, add a grain of thymol or a few drops 
of carbolic acid, filter, and make the total bulk 
up to 16 oz. or I,000 ccs. 


No. 1 Yellow Filter 
Stock gelatine solution 202. 120 ccs, 
Stock dye solution 24 mins, Sey 
Distilled water . vet Oetins 8 Bee 


No. 2 Yellow Filter 


Stock gelatine solution 2 oz. 120 ccs. 
Stock dye solution 48 mins. Gens. 
Distilled water . ] 144 tes 


No. 3 Yellow Filter 
Stock gelatine solution 2 oz. 120 ccs. 
Stock dye solution 96 mins, Eos 4, 
Distilled water . wt MEO ie Ea 


No. 4 Yellow Filter 
Stock gelatine solution 2 oz. 130" ccs. 
Stock dye solution . 192 mins. 24 ,, 


For every 16 sq. in. or 100 sq. cm. of glass 
allow 122 minims or 7 ccs. of the dyed gelatine, 
and two of each of the screens must be bound 


Colour Screen 


together. The increase in the exposure with the 
above filters for pinachrome or erythrosine bathed 
plates is No. 1 1-3, No. 2 I*7, No. 3 2°0, and 
No. 4 3:0 times. For commercial iso- ot ortho- 
chromatic plates—that is, those sensitised in 
the emulsion before coating—the exposure is 
about half as much again. 

The glass of which the screens are made should 
be selected patent plate, about ry in. thick, and 
it should be as parallel as possible ; for the best- 
quality screens optically worked glass should 
alone be used. In order to test the glass for 
parallelism of its sides, it should be placed on a 
sheet of black velvet and held at an angle of 
about 45° some distance from the cross-bars of 
a window, so that the reflection of these can be 
seen in the glass. On turning the glass round 
on the velvet, the image of the cross-bars will 
be seen to be double—that is, the reflection 
from both the front and back of the glass will 
be seen. These double images should, as far 
as possible, be constant in position one to the 
other, and not shift up and down or from side 
to side. The glass must be thoroughly cleaned 
and placed on a thick sheet of plate glass which 
has been accurately levelled, and the necessary 
quantity of dyed gelatine poured on to it, 
coaxed out to the edges with a glass rod, and 
allowed to set, when it can be put away to dry. 

It may be pointed out here that the position 
of the filter has some effect on the focal length 
of the lens and also on the definition of the 
image. When placed behind the letis it slightly 
lengthens the focus, but its effect on definition 
is a matter of actual test with every filter, 
though the nearer the filter is to the plate the 
less the effect; therefore, obviously, if placed 
in contact with the sensitive surface, the ques- 
tion of the quality of the glass is not of so much 
moment, and in this case even fixed-out and 
washed dry plates may be used. 

The cementing of colour screens is a messy 
process, and requires considerable practice to 
perform successfully. A fairly thick solution of 
Canada balsam in xylol, such as is used by micro- 
scopists, should be used, and the screens well 
warmed for at least half an hour, so as to ensure 
that they are thoroughly dry; the balsam 
should also be gently warmed. A pool of balsam, 
about half the size of the plate, should be poured 
on to one screen somewhat near one edge, and 
the other screen lowered first on to this edge 
and slowly allowed to fall down, when it will 
Squeeze the poo] of balsam out so as to cover 
the whole surface. Then a stout bulldog clip 
should be fastened on each side, and the screens 
put away in a warm place for the balsam to 
dry out; this will probably take four or five 
days. At first it is better to use excess of 
balsam, as this will be squeezed out and can be 
easily cut off when dry; but with experience the 
quantity of balsam may be reduced. 

The filters for three-colour work are innu- 
merable, the following being satisfactory :— 


Hoechst Dyeworks’ subtractive filters for 
three-colour printing of all kinds, 


Blue-violet Stock Solution 
Crystal violet o Oly gras irgog 
Warm distilled water 1202.1 55 mins. 350 ccs. 
Glacial acetic acid . 5-6 mins, 5-6 drops 


128 Colour Screen 
Filter 
Dye solution 338 mins, 20 ccs 
Gelatine solution (6 %) 34 Oz. 1004, 
or— 
Stock Solution 
Rapid filter blue I5$ gts. 1 g, 
Hot distilled water 6 oz. 160 mins. 180 ces. 


Tiquor ammoniz 


Filter 
Dye solution - 338 mins, 20 ccs. 
Gelatine solution 34 oz. ico 


This is faster to light than crystal violet, 


Green Stock Solution 


8 mins. 8-10 drops 


Rapid filter green I 62 gts, 4 g. 
Distilled water 34 Oz. 100 ccs, 
Filter 
Dye solution . - 338 mins. 20 ccs. 

Gelatine solution (6 %) 3402. Ioo ,, 


This transmits a narrow band in the extreme 
red; the following does not, and should always 
be used with panchromatic plates :— 


Stock Solution 


Filter blue green 154 grs, tg. 
Rapid filter yellow . 1 5+ ly ee 
Distilled water - 34% oz, TOO ccs, 
Filtey 
Dye solution . - 338 mins, 20 ces 
Gelatine solution (6 %) 34 02. 190 cee 
Red Stock Solution 
Rapid filter red I 77 gers. 5 g. 
Distilled water 7 Oz, 200 ccs, 
: Filter 
Dye solution : 8mins. 20 ccs, 
Gelatine solution (6 %) 34 Oz. 10O 4 


Allow 118 minims to every 16 Sq. in., or 7 ces. to 
every 100 qcm., and cement two glasses of each 
colour together. The ratio of exposures for 
pinachrome or pinacyanol bathed plates is, for 
the blue screen (yellow printing) negative, 4; 
for the green screen (red printing) negative, 
8-12 ; for the red (blue printing) negative, 8-12. 

For liquid filters the following, suggested by 
Newton and Bull, for use with panchromatic 
plates, with cells of 1 cm. internal thickness :— 


Blue Filter 
Victoria Blue B 


(Bayer) (1% sol.) . 448 mins, 47 ccs. 
Naphthol green (1% sol.) 174 os be et 
Distilled water to 20 02.” §1,000' *y 

This will not keep well when mixed. 
Green Filter 
Rapid filter green (1% 

sol.) ; i . 87 mins, 9 ccs. 
Naphthol green (1% sol.) 87 = Oxi 
Rapid filter yellow K 

(1% sob) sa, 5 age 9 4, 
Distilled water to 20 OZ. 1,000: ag 

Red Filter 
Rose Bengal (1% sol.) 442 mins, 84 ccs 
Rapid filter yellow K 

(1% sol.) 442 ,, 84» 

Distilled water to 20 OZ. I,000 ,, 


The above are to be used for the subtractive 


Colour Sensations 


process or three-colour printing, whether on 
paper or in the shape of superimposed stained 
transparencies for projection. For the pro- 
jection of transparencies by means of coloured 
lights or the additive process, the following should 
be used for obtaining the negatives :— 


Violet-blue Stock Solution 


Crystal violet . 62 grs. 32. 

Methylene blue 154 ,, ar 

Distilled water 8 oz. 384 mins. 250 CCS. 

Glacial acetic acid . 5-6 mins. 5-6 drops 
Filter 

Dye solution . - 338 mins. 20 ccs. 

Gelatine solution (6%) 3402. 100.0 

Green Stock Solution 

Rapid filter green 2 62 gts. 4 g. 

Distilled water 40z. 107 mins. 120 ccs. 
Filter 

Dye solution . . 338 mins. 20 ccs. 

Gelatine solution 4402." 1007.,, 


This transmits a narrow band in the red, but 
the following does not :— 


Stock Solution 


Filter blue green . 184 gts. I:2 g. 

Rapid filter yellow . 383 ,, 2°5 55 

Distilled water er. OR, 200 ccs. 
Filter 

Dye solution . - 338 mins. 20 ccs. 

Gelatine solution - 34 02. 100: 5}, 

Stock Red Solution 

Rapid filter red 2 . 77 grs. 5 g. 

Distilled water 7 OZ. 200 ccs, 
Filter 

Dye solution . - 338 mins. 20 ccs. 

Gelatine solution (6%) 34 oz. Tee ee 


The quantity of dyed gelatine per area is the 
same as for the subtractive filters, and two filters 
of like colour must be cemented together. The 
ratio of exposures with pinachrome or pinacyanol 
bathed plates is blue 4, green 12, red 12. 


COLOUR SENSATIONS 

Although there are considered to be but six 
or seven spectrum colours—red, orange, yellow, 
green, blue, indigo, and violet—they melt so 
insensibly one into the other that there are an 


Vv 
a 


roo 660 600 $50 500 40 400 


Curves Representing Actions of Various 
Spectrum Colours 


infinite number of distinct colours; again, in 

natural objects there are innumerable colours. 

It has been proved, however, that there are only 

three fundamental colours, that give rise to all 

the other colours by the excitation of three sets 
9 


129 


Colour Sensitising 


of nerve fibrils in the retina. This theory was 
enunciated first by Thos. Young (‘‘ Lectures on 
Natural Philosophy,’”’ 1807), and further elabor- 
ated by Clerk-Maxwell (Edinburgh Transactions, 
21,275, 1855), Von Helmholtz, Abney, Kénig, 
and others. The curves representing the respec- 
tive actions of the various spectrum colours, 
according to K6énig and Dieterici, are shown in 
the accompanying diagram, and represent the 
sensations excited in the retinal nerves by the 
three fundamental colours. There is some 
difference in opinion between physicists. as to 
the exact wave lengths of the fundamental 
colours, but there is not much error in the assump- 
tion that they are :— 


Red—extreme end of the visible spectrum 
about A 665. 

Green—A 507. 

Blue—a 475. 


The red sensation curve begins about A 680, 
reaches its maximum at A 575, drops strongly 
at A 490, with a slight rise again toward A 450, 
and ends at A390. The green sensation curve 
begins at A 680, rises to a maximum at A 550, 
and ends at A440. The blue sensation curve 
tises from A 580, rises sharply at A 480 with a 
maximum at A 450, and ends at A 390. 

The above may be considered as the now 
generally accepted theory of the colour sensations, 
but Hering suggested six fundamental colours— 
ted, green, yellow, blue, white, and black. This 
theory has not been accepted, but is interesting, 
as on it has been based a four-colour printing 
method (Zander). 


COLOUR SENSITISING 

It was very early recognised that certain 
colours acted more strongly on the photographic 
plate than others, and that the former were nearly 
all those that reflected the violet and blue 
spectral rays, which therefore were called the 
‘** chemically active ”’ or “ actinic,’ whilst green, 
yellow, orange, and red hardly produced any 
action at all. This view prevailed for many 
years, though Herschel pointed out in 1842 that 
it did not apply generally, as violet petals faded 
most quickly in green light and the other blue 
flowers faded most in yellow light, Draper 
enunciated the law that only those rays acted 
chemically on a substance which were absorbed 
by it. 

ae 1873 H. W. Vogel was examining various 
silver salts in the spectrograph and found that 
some English collodion plates, which had been 
stained with a yellow dye to prevent halation, 
were distinctly sensitive to green. Led by this 
fact, Vogel examined the absorptions of various 
dyes and then added them to collodion emulsion, 
and found that these also sensitised for the 
colours they absorbed. This principle was con- 
firmed by others, and soon after was successfully 
applied to commercial gelatine plates by Attout 
Tailfer, of Paris. 

The action of a very large number of dyes has 
been examined by various authorities, Eder, 
Valenta, Von Hiibl, Eberhard, Hinterberger, 
Ruh, etc., and the first-named, who has paid 
special attention to this subject, has formulated 
the following important conclusions: (1) The 
absorption spectrum of neither an alcoholic nor 


Colour Sensitising 


of an aqueous solution of the dye coincides with 
the position of maximum light action on the 
dyed gelatino-bromide of silver. (2) The maxi- 
mum of sensitiveness of the dyed silver bromide 
lies nearer, the red than does the absorption 
maximum of any solution. (3) The position of 
the maximum of absorption of the dye in gelatine 
and that of the maximum of sensitiveness of the 
dyed silver bromide differ generally by about 
thirty wave lengths; that is to say, those rays 
of light that are most active photographically 
on the dyed silvér bromide possess a mean greater 
wave length of about thirty wave lengths than 
those that are absorbed by the dyed gelatine 
{without the silver bromide). (4) The absorp- 
tion maximum of silver bromide dyed with 
eosine coincides exactly with the maximum of 
light sensitiveness on silver bromide dyed with 
eosine ; that is to say, those light rays which are 
absorbed by eosine-dyed silver bromide have the 
same wave length as those for which the dyed 
silver bromide shows the increased sensitiveness. 
(s) The dyes must stain the silver bromide grain ; 
the dyes that act vigorously are all “‘ substan- 
tive’? dyes. (6) They must show in the dry 
state—on dyed gelatine, or mofe correctly, on 
dyed silver bromide—even in considerable 
dilution, an intetise absorption band if they are 
to produce an intense action on the silver 
bromide. A natrow absorption band gives a 
natrow seusitising band. 

Although it has been established that a colour 
sensitiser must dye the silver bromide grain, yet 
all dyes that stain the silver bromide are not 
sensitisers. Neither fluorescence nor fugitive- 
ness to light plays any important part, as pure 
erythrosine is not fluorescent and yet is a power- 
ful sensitiser, and is fairly stable to light, whilst 
cyanine is very unstable and is a good sensitiser. 
Apparently, there is no connection between the 
chemical constitution of a dye and its sensitising 
powers, thouga Lumiére and Seyewetz have 
concluded that the sensitising action is con- 
nected in some way with the chromophoric group 
of elements. Joly has pointed out that all the 
sensitisers are photo-electric, and assumes that 
electrons are set free from the dye which act 
on the silver halides. 

Colour setisitive plates may be divided into 
practically two main classes, the commercial 
isochromatic or orthochromatic plate and the 
panchromatic plate. The former are usually 
prepared by adding erythrosine to the emulsion, 
either at the time of mixing or just before coat- 
ing, and are sensitive mainly to yellow-green and 
yellow, there being a characteristic gap or lack 
of sensitiveness in the blue-green. The pan- 
chromatic plates are neatly all made by bathing 
the finished and dried plates in a solution of the 
erythrosine. 

The method of introducing the dye into the 
emulsion has considerable influence on the result- 
ing colour sensitiveness. Those dyed in the 
emulsion—that is, before coating—have usually 
a lower x than plates bathed in a dye solution ; 
that is, they are less colour sensitive, though the 
reason for this is not apparent. 

Although excellent commercial colour-sensi- 
tive plates can be obtained, the following 
information may be useful. To sensitise for 
blue-green and green, up to about A 5,500, the 


130 


Colour Sensitising 
best dye is acridine orange NO, of the Leonhardt 
Farbwerke, Miihlheim. 


Stock Solution 
Acridine orange NO . 9:6 gfs, h gh 
Alcohol , 20 02, 1,000 ccs. 


Industrial alcohol may be used instead of the 


pure. The actual sensitising bath is:— 
Stock dye solution 4 OZ. 200 ecs, 
Distilled water to . 20 ;; 1,000". 


For greenish-yellow and yellow up to A 5,900, 
erythresine should be used, and the most suit- 
able dyes are bluish erythrosine of the Badische 
Anilin and Soda Fabrik, that made by Schu- 
chardt, of Gérlitz, or the pure dye of Meister, 
Iucius and Briining, of Hoechst. A stock 
solution is made of 1: 1000 of alcohol, ag with 
acridine; the sensitising bath is :-— 


Stock dye solution 4 OZ. 200 CCS. 
Liq. ammoniz (-880) . 96 mins. IDL yy 
Distilled water to 20 OZ. 1 OOO 5 


Erythrosine is an excellent sensitiser for the 
above region, but it leaves a minimum or gap 
in the bluish green, which, however, fills up with 
a generous exposure, so that it cam be used 
instead of acridine orange for all but P aaa 
work in the blue-green, and has the advantage 
of being more readily washed out of the gelatine, 
alcohol alone being able to remove the last traces 
of acridine. 

To sensitise for green, yellow, and red up to 
about A 6,200—A 6,400, one of the following 
should be used: orthochrome T, pinaverdol, 
pinachrome, or homocol, the action as red sensi- 
tisers being greater in the last two than the 
first two. A 1: 1000 alcoholic stock solution 
should be made, which should be kept in the 
dark; the actual sensitiser is— 


Stock dye solution 20 mins. 2 ccs. 
Distilled water 20 OZ. 1,000 ,, 


For the extreme visible red pinacyanol should 
be used in the same way. | 

For the infra-red, about wave length A 7,180, 
“little a,” as it is usually called, di ine 
should be used as above, only the stock solution 
must be added to the water at the very last 
moment, when everything is quite ready, and 
the plate immediately flowed with the dye, as 
the weak solution loses its sensitising power very 
quickly. 

The most convenient method of sensitising is 
by means of a grooved trough, into which, when 
filled with dye solution, the plates can be dropped. 
Or the worker may use a dish twice as large as 
the plates to be sensitised at one time. These 
are put at one end of the dish; the dish is 
tilted, and the dye solution poured into the 
empty end; then the dish is tilted back, so 
that the dye solution runs in an even wave over 
the plates. The dish should be gently rocked 
for three minutes, then the Yee removed and 
washed in a good stream of running water for 
three minutes, and set up to dry in a proper 
drying cupboard, or in at air-tight box comtain- 
ing a saucerful of calcium chloride. 

An alternative method of sensitising which 
considerably hastens the drying, is to replace 
two-fifths of the water in the above baths by 


Colour Sensitiveness 131 


acetone or methyl alcohol; the plates then dry 
in about half an hour in a warm place. 

The best panchromatic sensitiser is that sug- 
gested by R. J. Wallace. 


Pinacyanol (1: 1,000 sol.) 134 mins. 14 ccs. 
Pinaverdol (1: 1,000 sol.) 106 ,, SE 
Homocol (1:1,000 sol.) 106 _,, 4 ae 
Liquor ammonie . tl eee i ee 

_ Alcohol ; . Fin NEE BOOS. 4. 
Distilled water to Ss RE io. 2, 


The plate to be sensitised should be clean work- 
ing and with a fine grain, and therefore not too 
rapid. Care must be exercised as to the dark- 
room illumination and no light should be used 
for red sensitising. BE. j. W. 


COLOUR SENSITIVENESS 

Silver bromide precipitated in the form of an 
emulsion possesses great sensitiveness for the 
ultra-violet, the violet, and blue spectral regions. 
With an admixture of iodide of silver, precipitated 
at the same time, the sensitiveness extends 
beyond the bright blue slightly into the bluish 
green, but there is no practical sensitiveness to 
green, yellow, orange, or red. Sensitiveness to 
these regions is conferred on the silver halides 
by the addition of certain dyes to the emulsion 
in the making, or preferably by bathing the dry 
plates in aqueous solutions of dyes. It will be 
noted that the expression “no. practical sensi- 
tiveness’ is used, and this is employed for the 
specific reason that if the exposure is sufficiently 
prolonged, all the spectral colours will affect the 
silver halides, but the more actinic rays must be 
screened off by suitable filters ; it is not practical 
to give such prolonged exposures in the process. 


COLOUR SENSITOMETER 

A series of coloured glasses or dyed gelatines 
having special spectral transmissions, used for 
testing the colour sensitiveness of plates. Vidal 
constructed one of the first of these instruments, 
and the Chapman-Jones plate tester can also 
be used for the same purpose. Abney has sug- 
gested a somewhat similar instrument. They 
have not found extended practical application. 
(See ‘* Colour Sensitometry.’’) 


COLOUR SENSITOMETRY 

Soon after the introduction of the colour 
sensitive plate some method was found needful 
for expressing the added colour sensitiveness, and 
this was effected by exposing a plate in the 
spectrograph and estimating the densities by 
visual examination or merely drawing a graphic 
curve, a test of great unreliability, still further 
complicated by the fact that prismatic spectro- 
graphs were used. Later, plates were exposed 


to isolated patches of monochromatic light, a 


curve being obtained from the resulting negatives. 

This method was still further improved by using 

a spectrum and varying intensities of white light 
| obtaining an interpolation curve. 

The great disadvantage of the spectrographic 
method is that it is not capable of brief and 
commonly understood expression, and therefore 
many attempts have been made to obtain sensito- 
metric tests by means of charts of coloured pig- 
ments, which are open to the most serious 
objection that the pigmentary colours reflect 


Colour Sensitometry 


an enormous amount of white light, and whilst 
there is no object in nature that does not reflect 
white light, what the worker really desires to 
measure is the true increase in sensitiveness to 
a pure colour. Abney’s colour sensitometer and 
the Chapman-Jones plate tester consist of 
coloured glasses or gelatines of equal luminosity, 
transmitting either small or broad isolated 
patches of the spectrum, and the densities obtain- 
able can then be read and charted. Later, Eder 
and others divided the spectrum into three 
broad regions, the one including the blue and 
violet up to about A 5,000, which is practically 
the sensitiveness of the ordinary emulsion; a 
second region extending from the blue through 
the green to the yellow up to A 5,900; and a 
third, used only for panchromatic plates, extend- 
ing through the red. Eder’utilised the Scheiner 
sensitometer, and thus expressed numerically 
the actual ratio of speeds of the non-colour- 
sensitised emulsion and the added colour sensi- 
tiveness. 

This method has been still further extended 
by Mees and Sheppard to the Hurter and Driffield 
system, and is the most practical. The following 
are briefly the main features of it: the H. & D. 
sector wheel and the screened acetylene light 
(see “‘ Plate Testing ’’) are used, and between 
the light source and the sector wheel are inserted 
absorbent solutions which limit the active light 
to particular regions of the spectrum. For test- 
ing commercial iso- or orthochromatic plates, a 
yellow and a blue filter (Eder) are used; the yellow 
filter consists of a 4 per cent. solution of potas- 
sium chromate (not bichromate) in a thickness of 
tem. ‘The blue filter is a 2 per cent. solution of 
ammonio-sulphate of copper, also in 1 cm. 
thickness. The plate to be tested is exposed 
behind these two filters, and after develop- 
ment the inertias are found in the usual way, 
and the result or ratio termed x (chroma, a 
colour), and is— 


yellow inertia 
blue inertia 


blue sensitiveness 


= og : 
yellow sensitiveness 


For instance, a commercial iso plate was found 
to have an inertia of 0-34 behind the blue screen 
and an inertia of 4:8 behind the yellow screen ; 
then— 

yellow inertia 4-8 ___ blue sensitiveness 100 Ri 

blue inertia 0:34 yellow sensitiveness 7:1 

x 14. 

For panchromatic plates, it is essential to know 
also the increased sensitiveness to red; and 
Mees and Sheppard use three screens as follows : 
the blue screen is Eder’s given above, which 
passes the violet and blue up to A 5,000; the 
green screen, which passes from A 5,900 to 
A 5,000, consists of Eder’s chromate screen 
given above plus a screen of 1 cm. thickness 
of a saturated solution of copper acetate; the 
red screen is made with rose Bengal and tar- 
trazine :— 


Rose Bengal . « ne SEB. 5 a 
Tartrazine me SOR css LO 
Distilled water to . 20 02. 1,000 ccs, 
Gelatine . 728 grs. 73 g. 


Allow 20 minims, or 1°25 ccs., to every square 
inch of glass. 


Colour Test for Plates 


In all cases the screened acetylene light 
has been used, and whilst this does not give 
the absolute inertias of the plate, the ratios of 
colour sensitiveness are preserved. For three- 
colour work the actual filters to be employed 
may be used in the same way, and if an exposure 
be made without a filter the necessary increase 
of exposure for the blue-violet filter over the 
unscreened pia can readily be found. Con- 
siderable influence is exercised naturally upon 
the results obtained by the nature of the light 
employed, and one can easily understand that 
the standard light should be, if possible, daylight 
of constant spectral composition, or a secondary 
standard with as near as possible the same spec- 
tral composition ; for if the light be yellow, with 
a decided paucity in violet and blue rays, and 
corresponding richness in yellow and orange, the 
colour sensitive plate would show a much higher 
colour sensitiveness, which would be totally 
misleading. E. J. W. 


COLOUR TEST FOR PLATES (See “ Plate 
Testing.’’) 


COLOURING PHOTOGRAPHS, ETC. 

The three popular processes for colouring 
prints and slides are by means of aniline dyes, 
water colours, and oil colours. Colouring by 
the crystoleum process (which see) is also widely 
practised. Aniline dyes, although not so per- 
manent as water colours, have largely super- 
seded the latter, the dyes being so cheap and 
easy to use; they are also transparent, and allow 
the details in the pictures to show through them, 
whereas some water and oil colours are body 
colours which hide all detail. 

Photographs to be coloured with dyes or 
transparent pigments should not be deeply 
printed or given too warm a tone; but these 
points are of no importance when body colours 
are used. A desk of some kind, or an easel, 
will be required for large prints, but small ones 
may be laid flat upon a table or held in the 
hand. lantern slides and other transparencies 
are best held in the hand over white paper, or 
placed upon a retouching desk in such a way 
that the light comes through the slide, using 
preferably artificial light, as slides coloured in 
daylight are sometimes disappointing when 
viewed on the screen; transmitted light allows 
the density of the colours to be better judged. 
Sable brushes of the sizes known as No. o (very 
small) to Nos. 5 or 6 will be found the most 
serviceable for average work, but others, as 
experience dictates, may be found useful. 

Aniline Dyes.—These are the simplest of all 
colouts in use, and may be used for slides and 
all kinds of prints, although they appear to best 
advantage on ordinary P.O.P. (gelatine) prints. 
Suitable dye solutions all ready for use may be 
purchased, the colours being put upin cheap sets 
and itt very convenient form, Penny packets 
of dyes, obtainable at oil shops, are good enough 
for experimental work; to prepare them for use 
dissolve first in } oz, of acetic acid or vinegar 
and make up to 2 oz. with water. The raw dyes 
_ may be dissolved and prepared in the same way, 
but very little of the actual dye need be used, 
as they are very strong, and a few grains will 
make a large quantity of coloured solution. The 


132 


Colouring Photographs, etc. 


number of colours will depend upon the character 
of the work; clever colourists, it should be said, 
can get all the colours they want by using only 
three—blue, yellow, and red—as by mixing 
these in suitable proportions any colour likely 
to be needed can be produced ; blue and yellow 
make green; red and yellow, orange; blue and 
red, violet, etc. etc., the exact tints depending 
upon the proportions of the two colours. The 
average worker will prefer ready-made dye 
solutions, and the following will be found the 
most serviceable: Blue, yellow, brown, olive 
green, scarlet, purple, orange, and pink. These 
dyes may be combined if desired, green and 
orange, for example, making citrine; orange 
and purple, russet; etc. The secret of success 
in using aniline dyes is to have them weak, 
building up the colours required by repeated 
washes of the dye rather than attempting to 
obtain in one application a colour of full strength. 
So important is this that the beginner is advised 
to begin colouring with dyes near to a water 
tap, so that as the colours are put on they may 
be largely washed off under the tap, the opera 
tions being repeated until the desired strength is 
obtained. The process is really that of staining 
or dyeing the print rather than painting, as the 
last-mentioned term is generally understood. 
If the print is mounted and cannot be satis- 
factorily rinsed in water, the colours should be 
applied to the print very dilute, and immediately 
blotted with clean white blotting-paper. This 
prevents the dyes acting too quickly, and 
obliges the worker to proceed alee and build 
up the colour, Blotting-paper is not suitable 
for use on slides, and the slides should be repeat- 
edly rinsed instead, unless the dyes are applied 
sufficiently weak in the first instance. Prints 
do not usually require any preparation for 
colouring, but if much blotting or rinsing is to 
be done or the brush is at all stiff, it is advisable 
to harden gelatine films—P.O.P., bromide and 
gaslight papers and lantern slides—with a solu- 
tion of 1 oz. of formaline in 10 oz. of water; 
the fixed and washed slide or print is immersed 
in this for about ten minutes and then washed 
well. Alum should not be used for hardening 
previous to colouring with dyes, as it is apt to 
react chemically with some of the colours. 
Water Colours.—Water colours may be 
employed for all kinds of prints and slides. They 
differ essentially from dyes in that they do not 
sink into and stain the film, and therefore the 
surfaces need to be specially prepared so that 
they do not repel the colours; also, a medium 
is necessary for the colours in order that they 
may not dry dull and dead. A suitable applica- 
tion for prints is the following oxgall mixture :— 


Purified oxgall . . I5 gts. 6 g. 
Methylated spirit . - I 0Z 250 CS. 
Distilled water x »  £ jy eee 


This should be well mixed and applied to the 
surface with a broad, soft brush, and the print 
when dry will be in a proper state to take both 
water colours and even oil colours. This pre- 
paration is essential for albumen prints and 
others with a greasy surface, but may be omitted 
in the case of freshly-made P.O.P. or other 
gelatine prints, 

A suitable medium to use in place of water 


Colouring Photographs, etc. 


for the water colours is made by dissolving a 
small quantity of the best gum arabic in sufficient 
water to cover it, and adding two or three drops 
of glycerine. This is not necessary for matt 
surface prints. An albumen solution must be 
used as a medium when colouring albumen 
prints, and some workers use it for all kinds of 
glossy prints; it takes the place of the gum 
mixture, and is quite as good. The albumen 
mixture consists of the following :— 


White of egg. Ue Oks 30 ccs. 
Glycerine - 15 drops 15 drops 
Liquor ammonize A Sere i re 
Ammonium carbonate 20 grs. 13 g. 
Water 4 2 drms. 7 ccs. 


Whip the white of egg to a froth, allow to stand 
until clear, add the other chemicals previously 
dissolved in the water, and filter through muslin. 

The choice of water colours is an important 
item; there is a feeling in favour of colours 
in pans and not in tubes, but there is probably 
not much in the preference. Some are trans- 
parent, others semi-transparent, and others, 
again, are opaque or body colours. An expe- 
rienced worker may use any or all for print 
colouring, but for lantern slides transparent 
colours must be used. They are easily recognised 
by painting a few dabs upon glass and examining 
by transmitted light. Transparent colours are 
Prussian blue, crimson, alizarine yellow, Italian 
pink (which is really a yellow), olive green, sap 
green, purple madder and lake, and burnt car- 
mine. The opaque colours are light red, yellow 
ochre, scarlet lake, ultramarine, Naples yellow, 
burnt umber, and Vandyke brown. The semi- 
transparent colours are sepia, madder brown, 
raw and burnt sienna, cobalt, and bistre. The 
above list is not by any means complete, but 
contains enough for average work. When white 
is required, Chinese white and no other should 
be used. For faces of portraits the colouring is 
usually put on very weak in the form of cross 
hatching, but for all other work colours are 
brushed on in the usual way, using plenty of 
the medium so as to weaken the colours. 

Lantern slides can be coloured with trans- 
parent water colours, but they need no special 
preparation, although many consider it advis- 
able to harden them with formaline. Colours are 
Proce in broad, even sweeps, and but little 
difficulty will be experienced except in skies, 
which more often than not are plain glass. 
When the Prussian blue—really the only pigment 
available for the purpose—is put on the plain 
film, brush marks are likely to show, but this 
defect is remedied by dabbing the blue while 
wet very gently with the finger-tip, or with a 

iece of kid glove stretched over the finger. 

he sky may be stained an even blue with dyes, 
and then given character with water colours. 
The slides also may be chemically toned to 
various tints and then completed with water 
colours. Considerable practice is necessary for 
lantern-slide work, and no small artistic skill, 
if it is wished to avoid the banal effects fre- 
quently seen in commercial slides. 

O1i Colours.—Painting in oils, particularly upon 
enlargements, is chiefly a professional practice, 
and the method of doing the work depends to 
some extent upon the materials used. Trans- 


133 Colouring Photographs, etc. 


parent oil colours may be handled in a different 
manner from that adopted when body (opaque) 
pigments are used, The latter cover up the 
image, whereas the former, which give a rather 
weak effect, permit the shades and details of 
the picture to show through. For strength and 
high colouring the opaque colours are necessary, 
and for their use a knowledge of drawing and 
painting in general is requisite, as the photo- 
graphic image is simply used as a base. The 
colours which will be found of the greatest ser- 
vice are emerald green, Vandyke brown, indigo, 
Indian red, burnt umber, pink madder, light 
red, raw sienna, Naples yellow, yellow ochre, 
burnt sienna, crimson lake, raw umber, ultra- 
marine, flake white, and ivory black. 

Any kind of print may be coloured in oils— 
bromide paper being the most widely used— 
but owing to the oily nature of the colours it 
is necessary to size the print first in order to 
prevent the colours sinking into the paper, To 
make a suitable size, dissolve one pennyworth of 
clear patent size (obtainable at an oil-shop) 
in one pint of hot water, and when nearly cool 
give the picture a coat, and set aside to dry in 
a warm place. The coat of size must not be 
too thick, or it may peel off at a later stage and 
bring the colours with it. The brushes should 
be varied both in kind and size, according to the 
work, There should be provided stout hog-hair 
brushes, some thin badger brushes, and a few 
small sables; a badger softener is also useful. 
Megilp is used for thinning the colours, and a 
plentiful supply of turpentine should be provided 
for washing the brushes. 

The methods of applying the actual colours 
vary considerably. It is usual to apply a suit- 
able tint to the deepest shadows, and to work 
from this to the highest lights, using a more 
solid colour as the work proceeds, the reverse 
of water-colour painting. Drapery and costumes 
in portrait work may first be covered with 
transparent colour, working into it the various 
tints for the shadows, half-tones, and high lights. 
After the first tints have been put in, it is usual 
to let the canvas dry and to rub over with 
poppy oil, removing the excess with chamois 
leather; the more delicate colouring is then 
worked in. It is difficult to give precise in- 
structions for colouring, and the worker must 
to a large extent be guided by his own tastes. 
When the painting is completed it should stand 
on one side for a month before varnishing with 
copal or mastic, and in no case must the varnish 
be applied until the painting is dry. Copal is 
a hard and durable varnish, but mastic is widely 
used because it dries quicker and, if necessary, 
may be removed easily. 

For lantern slides transparent oil colours must 
be used. They are sometimes put on with a 
brush in the same way as water colours, but it 
is more general to dab on the colouring with the 
finger-tip. The best way of obliterating the 
grain of the finger-tip is to work upon the slide 
placed at different angles so as to cross the 
markings and break them up very lightly into 
a series of small dots. The finer details are 
best coloured by means of a fine sable brush, 
but too much colour must not be put on, as it 
is better to under-paint than over-paint, it 
being easier to add the colour than it is to take 


Coma 


it away. _ A useful dodge is to put the oil colours 
at first on the plain glass side, from which they 
may easily be removed if any error is made, 
or the colouring may be put on the cover glass 
of the slide. Parts of the slide may be coloured 
with dyes and parts with oil and water colours 
with good effect, but, no matter what process 
of colouring is adopted, some practice is neces- 
sary, patticularly with oils, which are the most 
difficult for a beginner to use satisfactorily. A 
slide for colouring in oil or water colours must be 
lighter and brighter than those for ordinary use, 
and it is important that they be dried in a room 
free from dust, as any specks or hairs upon the 
slide will show up very prominently when 
magnified upon the screen. PR 


COMA (Fr., Aberration zonale; Ger., Zonen 
abirrung, Nebeliger saum) 

Synonyms: oblique spherical aberration, zonal 
aberration. A defect resulting from the unequal 
magnification of the different zones of a lens, 
these zones being defined as imaginary circles 
dividing the surface of the lens into concentric 
rings. Asa result of coma the image of a bright 
point of light towards the margin of the field of 
view, produced by oblique rays, will be rendered 
as a comma- or pear-shaped blur—whence the 
name “‘Coma.’’ Coma may occur in a lens other- 
wise well corrected for chromatic and spherical 
abetration, and is approximately removed by 
careful design of the curves of the objective and 
precise selection of the different kinds of glass. 


COMBINATION PRINTING 

The art of making a print by the use of two 
or more negatives. The simplest form of com- 
bination printing is the printing of a cloud into 
a landscape, but combination printing proper 
is the art of adding trees, figures, or other objects 
to a picture, as practised by Rejlander, Robin- 
son, and other past masters of the art. Com- 
bination printing had its origin in 1855, when 
Berwick and Annan, of Glasgow, exhibited a 


picture printed from two different negatives—a 
figure in a landscape. In 1858 Sarony patented 
an improved process which consisted of taking 
up the different portions of the collodion film 
from the glass of one or more negatives and 
laying them down upon another glass in their 
proper relative positions and printing from it. 
Rejlander, however, was the first to draw 
attention to the possibilities of combination 
(printing, and in 1857 he used thirty negatives 


134 Combination Printing 


to produce a single picture (“‘ The Two Ways of 
Life’), which he exhibited at the Manchester 
Exhibition of that year; all except the part 
required was blocked out on each negative, all 
the negatives were then laid in turn upon sensi- 
tive paper and printed, thé remainder of the 
paper being covered with black velvet. In the 
following year (1858) Robinson produced the 
first of his famous series of combination prints, 
“Fading Away,’’ for which five negatives were 
used, and in 1863 “ Bringing Home the May” 
(nine negatives); this type of combination 
printing then became the craze. 

The methods fully described under “ Clouds, 
Printing in,’’ may be adopted in some forms of 
combination printing ; but in others, such as the 
addition of a figure to a landscape, or the sub- 
stitution of a suitable background for an unsuit- 
able in a figure subject, a different method will 
be more fitting (see, for example, ““Backgrounds, 
Printing in’’). In many cases, however, the 
pencil and brush marks described under the 
heading first given above will be found useful 
in securing registration. 

For combining portions of two or more nega- 
tives to form one print, whether the object is to 
print a new background to a figure or to combine 
in one picture selected parts of two or three 
landscapes, etc., the method described under the 
heading, “‘ Backgrounds, Printing in,” or some 
modification of it, cam be adopted. In some 
respects the method about to be described has 
points of advantage compared with that given at 
the reference last mentioned. A silver print is 
taken from the figure negative, and the figure 
cut out very carefully with a sharp knife. Both 
parts of the print must be kept to form masks. 
First, the portion from which the figure was cut 
should be attached to the glass side of the re 
negative, and then the two negatives sh be 
held together vertically with their edges resting 
on the table and the corners accurately coincid- 
ing, or preferably placed on a retouching desk 
with their corners together. The figure negative 
must be underneath and the glass side of each 
negative towards the worker. The figure that 
was cut from the rough print. must now be 
attached to the glass side of the background nega- 
tive in such a manner that it corresponds in 
position accurately with the opening in the 
mask on the figure negative, this opening being 
easily seen for obtaining a correct easier by 
this method of holding the two plates. ' 

In printing, it is immaterial which negative 
is used first. Hither negative is placed in the 
ptinting frame with one edge in close contact 
with the woodwork of the frame—preferably the 


edge that was testing on the table when the 


masks were adjusted on the negatives. In the 
diagram the edge aB is shown pressed closely 
against the frame, the corner being pressed right 
into that of the frame. The’ printing paper 
need not be cut accurately to fit the negative, 
but it must touch the same side and the same 
corner of the frame as the negative. The paper 
is indicated by dotted lines. When this part of 
the printing is finished, the print and the nega- 
tive are removed from the frame, and the second 
negative is placed in the frame with its corre- 
sponding side and corner pressed closely against 
the side and corner aB. The print is again 


a 
a i. 


Combined Development 


placed in position as before with the same side 
and corner touching the same parts of the 
frame, and the second part of the printing com- 
pleted. 

If the masks have both been accurately fitted 
to their respective negatives, the two parts of 
the print should join perfectly. Each print will 
show a soft outline due to the fact that the block- 
ing out is on the glass side of the negative, and 
these two outlines will slightly overlap and soften 
into each other in such a manner that, with 
reasonable care in fitting the masks and in print- 
ing, the junction will not show. When the block- 
ing out is on the film of the negative it is almost 
impossible to prevent the junction from show- 
ing as a hard and crude line, white in some 
places, dark in others. Masking on the glass side 
possesses the great advantage that it does not 
spoil the negative for other purposes. At any 
time the masking may be removed, leaving the 
negative uninjured. 


COMBINED DEVELOPMENT AND FIXING 
(See “Development and Fixing Com- 
bined.’’) © 


COMBINED LENSES 

When two lenses, such as the Zeiss single 
anastigmats, are combined to form a doublet, 
there is a simple formula for finding the focal 
length of the combination. It is to divide the 
product of the focal lengths of the two com- 
pouents by their sum minus the distance by 

ich ‘their optical centres or nodes of emission 
are separated. Thus, in the case of two lenses 
with focal lengths of 7 in. and 11 in. respectively, 
with a separation of 2 in., the focal length is 
arrived at as follows: 


7 x 31 ‘pee : 
y+il—2 ~ 16 = 4 ora 


If a positive and negative lens are combined, 
the focus of the negative lens is taken as a minus 
quantity, the calculation being otherwise the 
same. 

It is often necessary to find the focal length of a 
lens which when added to another of known 
focus shall produce a given focal length. Thus, 
a single lens having a focal length of 18 in. is 
to be used with another so that the focal length 
is reduced to 12 in. The rule is to multiply the 
focus of the lens of known focus by the focus 
desired, and to divide the product by the known 
focus less the desired focus. Taking the above 
example, the working is :— 

18 x i2 216 


Seis. 
No account of the separation has here been taken, 
but if absolute accuracy is desired with, say, 
a separation of 2 in., the formula is :— 


(18 xX 12)—2 214 : 
eo oe ee 


«See also ‘‘ Magnifier.’’) 


COMBINED REDUCERS 
Combined ’’) 


COMBINED TONING AND FIXING 
“Toning and Fixing, Combined.’’) 


(See ‘‘ Reducers, 


(See 


135 


Comets, Photographing 


COMETS, PHOTOGRAPHING 

The first attempt to portray the form of a 
comet was in the case of Donati’s comet of 1858, 
but the results were very imperfect, owing to 
the photographic processes being then in their 
infancy. The first useful photographic cometary 
records are of Tebbutt’s comet of 1881. The 
gelatine dry plate had been introduced, and 
with its increased rapidity, compared with the 
old collodion plates, the problem was much less 
formidable. Further improvements were made 
by the employment of large-aperture telescopes, 
chiefly of the reflector class. Inasmuch as the 
comet is generally moving very rapidly in a 
special orbit of its own, irrespective of the earth’s 
direction of rotation, the usual equatorial tele- 
scope is of little use unless special arrangements 
are made. To obviate the difficulty various 
schemes have been devised. The most success- 
ful, and the only one we need mention in a prac- 
tical treatise, is that employed by Prof. E. E. 
Barnard, of the Yerkes Observatory, near 
Chicago. He first makes a preliminary obser- 
vation to determine the rate of motion of the 
cometary nucleus, and its direction as pro- 
jected on the sky. ‘Then, attached to the eye- 
piece of his telescope, with which he follows the 
comet nucleus during exposure of the plate, 
he provides a fine spider thread fixed on a mov- 
able frame actuated by a delicate micrometer 
screw. If, now, he knows how far the comet 
will move on the ground glass of his camera in, 
say, a second, he has only to move this adjust- 
able cross-wire, set in the direction of the comet’s 
motion, by the same amount, and then by 
keeping the comet nucleus continually bisected 
by ‘the cross-wires, its image will of necessity 
be kept exactly on the same portion of the photo- 
graphic plate. It is a similar problem, but some- 
what more delicate, to that of taking a series of 
photographs of a moving object with a kine- 
matograph camera: the whole apparatus is 
usually traversed by means of a screw-and-worm 

ear. 

‘ For recording the whole phenomena attend- 
ing the passage of a comet, probably the most 
useful instrument is a wide-angle camera attached 
to a perfectly rigid form of equatorial mounting. 
Needless to say, the better the lens that is avail- 
able the better will be the resulting photographs, 
The modern wide-angle anastigmat is the ideal 
instrument, and as in these cases it is an object 
of definite area that has to be portrayed, the 
greater the ratio of aperture to focal length the 
shorter will be the time of exposure necessary to 
obtain a satisfactory image, and in consequence 
the risks of failure due to vibration or bad 
weather will be minimised in proportion. 

The plates used should certainly be backed and 
panchromatic, as a considerable proportion of 
the cometary light is green and yellowish-green, 
and this is all ineffective if ordinary plates, sen- 
sitive only to the blue and violet, are employed. 

Development should be very carefully per- 
formed, as in general the range of gradation 
will be very great, varying from the intensely 
brilliant nucleus to the filmy streamers constitut- 
ing the delicate tail. The developer may be 
pyro soda, rodinal, metol, or metol-hydroquinone, 
but the developers giving excessive density with- 
out the full scale of detail should be avoided. 


Compass, Photographer's 136 


COMPASS, PHOTOGRAPHER’S (Fr., Bous- 
sole horaive; Ger., Photographischer Kom- 
pass) 

A magnetic compass the dial of which is ar- 
ranged to indicate the time of day when the 
subject, in any given direction, will be most 
favourably lighted for photography. 


COMPENSATING EYEPIECE (See “ Eye- 
pieces.’’) 


COMPENSATION FILTER 

A screen (generally yellow) for cutting off 
excess of ultra-violet, blue, and violet rays (see 
also “‘Colour Screen or Filter”’). In process 
work it is used largely in colour work, especially 
with collodion emulsion, it obviating excessive 
staining of the emulsion in cases where the latter 
is stained by the addition of a dye. 


**COMPENSATOR ”? NEGATIVES 

A system advocated by Newton Gibson and 
published in April, 1905, for preventing hala- 
tion without backing and controlling contrasts 
when taking difficult subjects, particularly 
imteriors. The method is to place a dry plate, 
glass side towards the lens, in the camera and 
to give a very short exposure in order to secure 
the high-lights and not the shadows; the plate 
is then developed, fixed, and dried. When 
quite dry the under-exposed negative is placed 
in the dark-slide in contact (film to film) with 
another dry plate, and the same view taken 
again through the compensator negative, taking 
care to givea full exposure for the shadows. If 
the first negative is of the right density, the 
second will develop in good gradation, the win- 
dows and other high-lights not being over- 
exposed and too dense, because of their being 
covered by the compensator through which the 
light has to pass to act on the second plate. 
Obviously the camera must not be moved in the 
slightest degree between the two exposures, or 
the picture will not be in register; and the 
system is therefore out of the question where the 
eamera cannot be left untouched for some time. 
Success depends mainly upon the accuracy of 
register, and the relative amount of exposure 
and development necessary for the compensator 
negative and for the final negative. It is possible 
to over-correct the highest lights by making them 
so dense on the first negative that light will not 
go through them. 

The process can be adapted to existing faulty 
negatives. A thin positive is made by contact 
on celluloid film, and when developed and dry 
it is bound or cemented to the negative in the 
position occupied when printing. The thick- 
mess of the celluloid film between the negative 
image and the sensitive paper when printing 
will cause no trouble if a fairly concentrated 
light, entirely from the front and not from the 
sides of the frame, is used for printing. 


COMPOSITE, ANALYTICAL, OR 
‘‘AVERAGE’”’ PORTRAITS 

A style of picture made by taking several 

portraits of the same size upon one plate, or 

by printing from several portrait negatives 

tpon one piece of paper, the result being sup- 

posed to give a type of the whole. Such pic- 


Composite Portraits 


tures are claimed by some to be of scientific 
value to students of anthropology, but they are 
more generally looked upon as curiosities, About 
the year 1887 they were popular in the United 
States. Their origin is said to be due to a con- 
versation between Herbert Spencer and Francis 
Galton about the year 1876, and Darwin also 
had some correspondence on the subject in 1877. 
The original idea was to have heads of two 
different people, one upon each half of a stereo- 
scopic picture, and to combine the two in a 
stereoscope, which method serves admirably ; 
but not more than two different heads can be 
combined in this way, whereas by taking nega- 
tives specially for the work any number of faint 
images of several portraits in succession can be 
obtained on one plate, finally developing the whole 
as one portrait. If reasonable care is taken in the 
making of such a composite negative there is 
seldom anything about the composite picture 
to indicate that it is not a mere portrait of an 
individual, whereas, of course, it is a com- 
bination of the portraits of several. Full or 
three-quarter faces make the best composites, 
and before beginning the work the focusing 
screen should be marked where the eyes, nose, 
and mouth are to be upon the screen, the mark- 
ings being made when the first sitter is posed 
and focused. The images of the sitters which 
follow must be adjusted to those lines; and as 
there is a variation in the distances between 
eyes, nose, and mouth, the camera has to be 
adjusted after each partial exposure. The total 
time of exposure must be divided up between 
the number of sitters. If, for example, the time 
required for an ordinary portrait is three seconds, 
and it is required to make a composite portrait 
of three sitters, the exposure in each case will 
be one second. When the number of sitters is 
relatively great, the lens must be stopped down 
to allow of increased exposure being given. 
For example, in making a composite portrait of 
six sitters, it would be better to use such a 
small stop that the exposure would be increased 
to, say, twelve seconds, when each sitter would 
be given two seconds. The lighting should be 
the same throughout, and it is also advisable to 
have a dark covering over the shoulders and 
round the neck, instead of white collars, fancy 
ties, blouses, etc., so as to obtain a uniform 
effect. 

An inferior method is to copy a series of por- 
trait prints upon one plate so as to get one 
negative of the whole; and another is to make 
transparencies from several portrait negatives 
(if they match properly) and make one negative 
from them by contact or through the camera, 
printing or copying each in turn so as to get 
a negative of the whole, by a series of partial 
exposures. 

Probably the most famous of all composite 
portraits was that produced by Oliver Ljip- 
pincott, of New York; it included portraits of 
fifty-one bank managers, and took from Decem- 
ber 10, 1908, to July 27, 1909, to complete. 
All were taken full face, and all eyes and pupils 
were registered, irrespective of the size of the 
head. Positives were made from the original 
negatives—all of which were taken separately— 
by means of prismatic reflectors and a twelve- 
power magnifying glass, and registered accurately 


F 
4 


\ 


Composition, Pictorial 


upon the screen. Every fourth positive was 
again converted into a negative, and every fourth 
negative again into a positive, the process being 
repeated until the final negative was arrived at, 
and the whole of the fifty-one individuals con- 
verted into one portrait. Lippincott states 
that it took 783 negatives and positives to 
accomplish the work, and, deducting failures, 
it took 553 positives and negatives to complete 
the one picture, which was widely published 
under the title of ‘‘ The King of Finance.’’ 

Composite prints of a sort may be made from 
existing portrait negatives if they happen to 
match in posing, lighting, and size. P.O.P. is 
used and the first negative partly printed, the 
remaining negatives being then printed in turn 
upon the one piece of paper, and the print finished 
in the usual way. 

There is a kind of composite photography (not 
portraiture) frequently employed in the pro- 
duction of picture postcards. Figures are cut 
out from different prints, stuck upon the same 
base, and copied, in this way obtaining many 
ae but worthless, inartistic, and untruthful 

ects. 


COMPOSITION, PICTORIAL 

Composition is the placing or arrangement of 
the different component parts of a picture in 
such a manner that the result is pleasing and 
harmonious. Much has been said and written 
about the so-called “laws ”’ of composition. The 
use of the term “‘laws’’ is hardly justifiable. 
Even the most definite and emphatic rules may be 
broken with impunity, frequently to the advan- 
tage of the result. The most that can fairly be 
said is that some arrangements are found to 
be more pleasing than others in the impression 
they create. By studying the elements of these 
more pleasing arrangements certain generalities 
ate deduced, but these should not be dignified 
by the name of laws. 

It is safe to say that the best pictorial work is 
not the result of a rigorous application of some 
clearly defined code of “‘laws.’”’ It is rather the 
outcome of a kind of instinct, a natural feeling 
for what is harmonious, tasteful, and pleasing. 
Whether that instinct can be created is very 
doubtful; but it can certainly be fostered and 
cultivated by careful study of Nature, and of 
graphic representations of Nature produced by 
others who have themselves studied and ob- 
served. Thus will be produced a perception or 
sense that certain things are “‘right’’ and that 
others are “‘wrong’’; and efforts can then be 
made to secure the right and avoid the wrong. 

The natural limitations of photography 
impose severe restrictions on the worker in his 
attempts to secure what he considers to be good 
composition. Apart from combination printing 
and certain limited means of modification, he is 
almost confined to selection of subject and point 
of view to secure the result he desires. He 
should by all means familiarise himself with any 
available expedients that may assist him to 
reach the desired goal, but to a great extent he 
will have to content himself with what is before 
him rather than what he would wish. 

Nevertheless, it may be helpful to give a few 
examples of what is, in a general way, to be 
sought for or avoided. A picture should contain 


137 


Compressed Gas 


one principal object, or group of objects, which 
should not be placed too far from the middle of 
the space. Everything else should be comple- 
mentary and subordinate to this. Two or more 
objects of equal importance will distract the 
attention and produce a lack of unity. The eye 
should be led or attracted to the principal 
object—there should be nothing that forms a 
kind of barrier. There should be no strong 
patches of light, or anything else that irresistibly 
attracts the eye, at the edges of the picture. 
Neither should lines lead out of the picture or 
to the unimportant parts of it. Detached patches, 
either of light or shade, should not be scattered 
about over the space. The horizon line should 
not bisect the picture, neither should the space 
be divided into halves diagonally. One mass 
may advantageously be repeated by another 
similar but subordinate. Upright lines may be 
contrasted with, and broken by, horizontal ones ; 
and a line leading in one direction may be 
balanced by one running in the opposite direc- 
tion. Balance, however, should not be too sym- 
metrical and formal, An arrangement of masses 
that forms a rough triangle with the apex towards 
the top of the picture is generally effective; as 
is also one in which the main lines radiate from 
the principal object. 

Such general suggestions as these might be 
extended to great length. But no multiplication 
of them, or knowledge of them, will of itself 
be sufficient to ensure the production of pictures 
of satisfactory composition. Patient and care- 
ful study and analysis of pictures of acknow- 
ledged merit will be found interesting and help- 
ful. It will aid in forming ideas as to the means 
by which certain satisfactory results may be 
obtained, and will strengthen those faculties of 
judgment and good taste without which the most 
elaborate series of rules of composition will be 
of no avail. (See also “‘ Lines in Composition.”’) 


COMPOUND LENS 

An almost obsolete term used to denote the 
difference between the single or landscape lens 
and the double or triple combinations composed 
of more than one cemented element. 


COMPRESSED CHEMICALS 

For convenience of catriage when touring, 
many photographic chemicals are now obtain- 
able either. compressed into small glass or card 
packages or in the still more portable form of 
tablets, ‘‘ tabloids,’’ ‘‘scaloids,” etc. The advan- 
tage of this method of packing chemicals, besides 
the small amount of room that they occupy, is 
that the worker is quite certain of having pure 
standard reagents, which only require dissolving 
in water to form the usual photographic solu- 
tions. 


COMPRESSED GAS 

For producing the oxy-hydrogen light (lime- 
light), a hydrogen flame, supplied with oxygen 
under pressure, plays upon a small cylinder of 
lime, a spot on which is heated to incandescence. 
Some years ago the lanternist had to manu- 
facture one or both of the gases employed, but 
the method is now obsolete, and it is usual to 
obtain the gases, compressed into steel cylinders, 
from one of the companies who make a specialty 


Concave Lens 


of supplying them in this form. Photographic 
dealers and pharmaceutical chemists are gener- 
ally prepared to obtain compressed gas to order, 
the charge being so much per cubic foot. Each 
cylinder needs to be fitted either with an auto- 
matic regulator, which will adjust the supply of 
gas to requirements, or with a reducing valve 
{see also ** Cylinder, Gas’’). To obtain the best 
results with a mixed jet, both the oxygen and 
the hydrogen should be under pressure, although 
an experienced lanternist can get good results 
with a mixed jet supplied from the gas main 
and from a cylinder of compressed oxygen. 
For ejector and blow-through jets, only the 
oxygen need be under pressure. For determining 
the content of a cylinder, a pressure gauge is used. 

Compressed acetylene (the gas is dissolved 
under pressure in acetone) is obtainable, and can 
be used for lantern purposes. 


CONCAVE LENS (Fr., Leniille concave; Ger., 
Hohilinse) 

A lens that is depressed or hollowed ont; 

known also as a divergent lens. When two faces 

are concave, as at A, it is described as ‘‘ concavo- 


C. Concavo- 
plane Lens 


B. Concavo- 
convex Lens 


A. Concavo- 
concave Lens 


concave ’’’; when one is concave and the other 
convex, as at B, it is ““concavo-convex’’; and 
when one of the faces of a concave lens is 
plane, as at C, it is “concavo-plane.” The 
“biconcave lens’’ is the ‘‘ concavo-concave.’’ 
The ‘‘concavo-convex’”’ is also known as a 
“‘meniscus’’ lens. 


CONCENTRIC LENS 


A lens patented in 1888 by Dr. Schroder and 
introduced in 1892 by Ross, being perhaps the 
eatliest application of the new Jena glasses in 
Great Britain to photographic work. It is com- 
posed of two symmetrical combinations, each 
consisting of a plano-convex of glass of high 
refractive but low dispersive power, and a plano- 
concave of low refraction but higher dispersion 
than that used for the convex lens. The two 
plane surfaces are cemented and the inner and 
outer curves are concentric; hence the name. 
The lens has an excellent flat field over a wide 
angle, and is still esteemed for copying. 


CONCENTRATED SOLUTION 


A solution made up very strong, chiefly in 
the form of a stock developing solution, and 
needing to be diluted with water before use; 
it may or may not be saturated. It is not 
Synonymous with saturated solution (which see), 
although sometimes thought to be so. Rodinal, 
certinal, azol, and similar developers are con- 
centrated solutions. The single-solution devel- 
oper given under the heading “ Adurol” is a 
good example of a concentrated home-made 
developer. Concentrated solutions are handy 


138 


Condenser 


for storing ; they do not take up so much room 
and asa rule keep better. Almost any developer 
with which the worker is instructed to take 
equal parts of Nos. 1 and 2 (or A and B) may 
be made in a more concentrated form by simply 
using half the water given in the formula, and 
adding the other half at the time of using. 
Hydroquinone cannot in the ordinary way be 
made up in a highly concentrated form, but for a 
** ten per cent.” formula see ‘‘ Hydroquinone.”’ 

Toning baths are not, as a rule, made up in a 
highly concentrated form, because of the danger 
of the gold precipitating, particularly when sul- 
phocyanide is used; the following, however, has 
been recommended for the use of workers whose 
dark-room space is limited and who wish to 
keep a highly concentrated bath :— 


Gold chloride 84 grs. 4°8 g. 
Strontium chloride. 85 ,, Sia 
Distilled water I oz. 250 ccs. 


Heat the water to 200° F. (93° C.), add the gold, 
and then the strontium. Next add 7 drms. of 
water in which 25 grs. of potassium sulpho- 
cyanide have been dissolved. Heat again to 
the same temperature as before, filter, and 
make up to 2$ oz. with water. This is highly 
concentrated, and keeps well; when a toning 
bath is to be made up for use, add 4 oz. of the 
concentrated solution to 5 oz. of water. 


CONDENSATION 
tion on.,’’) 


CONDENSER 


In optical projection the condensing lenses 
cause the rays of light emitted by the lamp or 
jet to pierce the transparency from all points, 
the rays being then transmitted to the objective 
or focusing lens. Diagram A shows the general 
optical system by which projection is accom- 
plished, E being the illuminant, F condenser, G 
transparency or slide, and H objective or focus- 
ing lens. The condenser shown is the one com- 
monly used. Light rays, unless intercepted, 
always travel in straight lines and, as indi- 
cated at EH, in straight lines from their source. 
This holds good, no matter whether the illu- 
minant be oil, limelight, acetylene, or electric 
light. For the purposes of optical pe 
it is necessary to collect a large angle of these 
rays, transmit them through the slide, and pass 
them on to the projecting objective, by means of 
which a large image is brought to a focus upon 
the screen placed at some distance beyond. 


(See “Lenses, Condensa- 


A. Optical System of Optical Lantern 


In cases where the illuminant may be regarded 
as a point, such as with the limelight or electric 
arc, many experts consider that the Herschel 
form of condenser B possesses advantages. Many 
years ago two lenses of somewhat long focus and 
shaped as at C, were employed, but this form has 


Conjugate Foci 


long been obsolete. The forms shown at A, B, 
and C are capable of collecting a fairly large cone 
of rays; the lens next the light serves as the 
collecting lens and for transmitting the rays to 
the second lens, which bends and converges 
them towards the objective, as at A. The dis- 
tance of the illuminant from the condenser 
governs the angle at which the rays are sent on 
towards the objective. The triple form of con- 
denser D possesses many advantages for micro- 
scopic and other scientific work, inasmuch as it 
collects a greater angle of light. 

In the best condensers the lenses are ground 
to a sharp edge. The lens next to the illuminant 
unavoidably gets very hot, and hence should be 
mounted loosely in the cell, for if at all tight it 


B. Herschel ©. Condenser D. Tripie-lens 
Condenser with TwoLong- Condenser 
focus Lenses 


‘will, in expanding with the heat, become cell- 
bound, and a crack will probably result. One 
method of ‘preventing this is to provide the 
mounts with three or four spring clips or spring 
rebates, which allow of the expansion of the 
glass and also of ventilation. The intense heat 
atising from powerful arc lamps, such as are 
mecessary in kinematograph projection work, 
tends to overheat the lenses in a very short time, 
and the danger of breakage is therefore increased. 
Several makers, recognising this fact, have pro- 
vided means for the ready removal of the con- 
densers from their cells, so that fresh ones may 
be substituted at intervals during a display, and 
this without serious interruption. When using 
all forms of condensers, sudden cold draughts 
must be guarded against, or cracking will almost 
certainly occur. 

The bull’s-eye condenser, as used in photo- 
micrography, is described under its own heading. 


CONJUGATE FOCI (Fr., Foyers conjugués ; 
Ger., Konjugierte Brennpunkie) 

The distances between lens and object, and 
lens and image ; known respectively as the major 
and minor conjugate. They are always pro- 
portional to the ratio between the size of the 
‘object and that of the image. Thus, in enlarg- 
ing from quarter-plate to whole-plate—a ratio 
of 2—the major conjugate, or distance between 
lens and bromide paper, will be twice the dis- 
tamce between lens and negative. If F = focal 
length of lens and R = ratio, then, whether 
enlarging or reducing, F x (R + 1) = the greater 
distance, or major conjugate; and the major 
conjugate + R =: the lesser distance, or minor 
conjugate. If, however, the image is full-size, 
the conjugate foci are each equal to twice the 
focal length of the lens, 


CONTACT BREAKS ’ 
- Mechanical devices for automatically “‘mak- 
ing’ and “‘ breaking’”’ the current flowing through 


139 Continuing Action of Light 


the primary winding of an induction coil (which 
see). Several forms of contact breaks arein use, the 
most popular being the hammer, electrolytic, and 
motor-mercury breaks. The first-named con- 
sists of a metal spring carrying a soft iron head 
and pressing against a platinum point which 
completes the circuit when no current is passing 
through the coil; but when the current is 
switched on the soft iron core becomes a magnet, 
attracts the block of soft iron, and draws the 
metal spring from the platinum point, thus 
“breaking ’’ contact. The metal spring or 
“hammer” rapidly vibrates, “ making” and 
“breaking ’’ contact while the coil is working. 
In the electrolytic break, the current is com- 
pleted by a platinum point projecting from a 
porcelain cylinder immersed in an electrolyte. 
When the current is turned on, electrolytic 
bubbles immediately form round the metal point 
and break the circuit; the bubbles disperse, and 
the contact of the platinum with the water again 
completes the circuit. The rapidity with which 
the bubbles form and disperse makes the electro- 
lytic break a highly efficient one. The motor- 
mercuty break consists of a jet of mercury 
rapidly revolving in a sealed chamber with two 
or more strips of metal fixed in the sides. When 
the jet strikes a metal strip the current flows 
through the coil; when the metal is passed the 
contact is broken. 

Contact breaks make and break the flow of 
electricity through the coii from a few hundred 
to several thousand times a minute. In X-ray 
work an efficient contact break is of the highest 
importance. 


CONTACT, OPTICAL (Fr., Contact optique ; 
Ger., Optische Beriihrung) 

When two substances are cemented so closely 
together that there is no air space between, and 
the four surfaces have apparently been reduced 
to two, they are said to be in optical contact. 
A typical example is a pair of lenses cemented 
with Canada balsam; while the silver coating 
on a mirror affords another instance. To mount 
prints in optical contact is to cause them to 
adhere to suitable glasses, usually bevelled, by 
means of a warm solution of gelatine. Prints 
mounted in this way are often known as opalines, 
presumably. because they sometimes have a 
margin of white paper, which, when seen through 
the glass, resembles opal. (See also ‘‘ Opalines.’’) 


CONTACT PRINTING AND CONTACT 
PROCESSES 

All printing papers and lantern slides may be 
printed by contact, the term indicating the 
placing of the sensitive surface of the paper or 
plate to be printed upon in contact with the 
film side of the negative. The alternative 
method is that of printing by enlarging or 
reduction through a lantern or camera. 


CONTINUING ACTION OF LIGHT 

This action occurs only in the carbon and 
kindred processes of photographic printing ; 
that is, in those that depend on the fact that 
gelatine and other colloid substances become 
insoluble when impregnated with an alkaline 
bichromate and exposed to light. The process 
of rendering insoluble, once begun by exposure 


Contrast 


to light, continues after the print is taken from 
the frame, even if stored in a perfectly dark 
place, so that a partially exposed print may be 
completed by this continuing action. It is, 
however, very slow and uncertain. It depends 
on the presence of dampness in the air; and, 
consequently, it is much more rapid in wet 
weather than in dry. This continuing action 
may be entirely prevented by storing the print 
in an absolutely dry receptacle, such as a calcium 
storage tube used for the platinotype process. 
When prints can be developed within a few hours 
from the time that they are taken from the 
frames, the keeping of them under moderate 
pressure between dry blotting-paper is sufficient 
to prevent any appreciable increase in depth. 


CONTRAST 

The range of tones in a negative or print, 
from the highest light to the deepest shadow. 
A print is said to be flat or lacking in contrast 
when the highest light is a pale grey, the deepest 
shadow a medium grey only, and the gradation 
between the various tones is very slight. A 
pe possesses good contrast when the highest 
ight is either pure white or a very pale tone, 
the deepest shadow a rich black, and well-marked 
gradations separate the various details and tones. 
In nature the range of contrast may be from 
one to several hundreds; in a print on matt- 
paper the range from pure white to deep black 
is about one to twenty-five. In a highly glazed 
print the range may extend from one to fifty. 


CONTRAST, EXCESSIVE 

This may exist in a negative or print when 
the scale of tones is too long for the sensitised 
film to record satisfactorily. The darker tones 
will be a mass of black, since the deepest have 
gone beyond the deepest tone of the paper, while 
the lighter tones will be a mass of plain white 
without detail. A familiar example is the blank 
white sky that is frequently seen in a print when 
the sky portion of the negative is over-dense. 
Reduction is the proper treatment for an over- 
dense negative. (See other headings, in par- 
ticular “* Bennett’s Reducer.’’) 


CONTRETYPE NEGATIVE 

A negative produced by sensitising a gelatine 
plate with potassium bichromate, drying, expos- 
ing under an ordinary negative, and soaking 
in water containing Indian ink or any coloured 
dye. The colour is absorbed by those parts of 
the gelatine not affected by light; and in this 
way, after fixation, is obtained a duplicate of 
the original negative, but reversed. 


CONTROL IN PRINTING 

Methods of treating negatives, or methods of 
treatment adopted while printing, may be 
summarised under the above heading. The 
object in all cases is the same; namely, to pro- 
duce a better, a more harmonious, or a more 
satisfactory print than that which the negative 
would give if the ordinary course were pursued. 
It is quite incorrect to assume that it is only 
inferior or imperfect negatives that require 
such assistance. The more critical the worker 
becomes with regard to his results, the more 
will he adopt methods of control. In a large 


140 Control in Printing 


proportion of subjects, the lighting or other 
conditions may render the resultant negative 
inharmonious—not necessarily harsh or imper- 
fect technically, but inharmonious in the sense 
of there being strong lights, or emphasis, in parts 
where such strength is detrimental to the general 
effect. It is control for securing true balance 
of light and shade, and for obtaining the most 
artistic result, that is the object of the treatment 
described. 

The most simple method of control consists in 
shielding those parts of a negative which tend 
to become too dark, while the remainder of the 
print attains its full strength. In some cases 
this may be a simple shielding of a small corner 
or one end, while in others it may be necessary 
to shield almost the entire plate while a small 
part prints out fully. In printing by diffused 
daylight, a piece of thin wood or card may be 
supported at about 4 in. or 1 in. above the sur- 
face of the negative, and covering those parts 
that attain their full depth too soon. The light 
diffuses gradually under the edge of the shield, 
grading softly from full action through the un- 
shielded portions to practically no action at all 
under the greater part of the shield. The manner 
in which the change is effected, the sudden or 
the gradual transition from full printing to no 
action at all, will be determined by the distance 
of the shield from the negative. Even if as 
close as 4 in., no line or sudden mark will show. 
In the case of a bright window in an interior 
photograph, a hole may be cut in a sheet of card, 
and the card supported above the negative so 
that the hole is exactly over the window, allow- 
ing its details to print out fully while the other 
parts are restrained. The effects of slight hala- 
tion may be entirely removed in this manner 
without any work on the negative. 

In printing by artificial light, the same results 
may be obtained byjkeeping the shields in motion 
while they are in use. By that movement, the 
risk of a sharp line showing is entirely obviated. 
The greater the extent of the movement of the 
shield, the softer the transition of its effect. 

A second method, which is very useful in those 
cases in which there is a well-marked line in 
the subject at which the change in strength of 
printing should be made, consists in coverin 
the glass side of the negative with very thin 
tracing paper or ground-glass varnish. The 
paper or varnish is cut away from those parts 
that print too slowly. The tracing paper to 
employ is that sold by artists’ colourmen under 
the name of papier végétal, or vegetable tracing 
paper. It is very thin and translucent. It 
should be slightly damped and attached to the 
glass at the margins by a little gum. When dry, 
parts may be cut away as desired, the edges of 
the cut parts being secured by a touch of gum. 
Matt varnish is finer in character, but more 
difficult to apply. The degree of restraint pos- 
sible may be increased by using a yellow-tinted 
varnish. The extent to which parts of a negative 
are held back in printing by this method is not 
great, but still sufficient for all ordinary nega- 
tives. A negative that has been prepared in 
this manner can be printed quite successfully by 
artificial light by the ore is expedient of ceeping 
the frame moving slightly during the exposure. 
In diffused daylight, no movement of the frame 


Convention, The Photographic 


is necessary, the thickness of the glass plate being 
sufficient to diffuse the light and prevent hard 
lines showing at the edges. 

A third method of controlling results consists 
in cutting out a mask that will fit exactly those 
parts which require holding back. The most 
satisfactory way of making the mask is to take 
a silver print from the negative, and, having 
-eut out the parts that print too quickly, to fix 
them to a piece of plain glass the same size as 
the negative. They should be put on in such a 
manner that when the glass is laid exactly over 
the negative the cut pieces will be in the pre- 
cise position necessary. The printing is com- 
menced in the usual manner, and as soon as 
the parts that correspond with the mask are 
sufficiently dark, the glass that bears the cut-out 
pieces is placed in position, care being taken that 
the corners coincide with the corners of the nega- 
tive, thus ensuring that the mask is exactly in 
position. Although it involves more trouble 
in ptinting than does the use of tracing paper 
or matt varnish, this method possesses the 
advantage of allowing any degree of restraint 
to be exercised. 


CONVENTION, THE PHOTOGRAPHIC 

The Photographic Convention of the United 
Kingdom was founded in the summer of 1886, 
Its object was to afford facilities to photo- 
graphers, professional and amateur, for an 
annual gathering at some suitable town pre- 
viously agreed upon, for the purpose of hearing 
and discussing papers of photographic interest, 
of holding exhibitions, social outings, etc. ‘The 
founders were the late J. Traill Taylor and 
J. J. Briginshaw. 

Conventions carried out on this model, but on 
a much larger scale, have long been popular 
amongst photographers in the United States. 


CONVERGENT DISTORTION (See “ Distor- 
tion.’’) 


CONVERGING LENS 

‘A positive lens, or one capable of bringing 
tays to a focus; a convex lens, In practice al 
convergent lenses are convex, or thicker at the 
centre than at the edges. 


CONVERTIBLE LENSES 

The single components of a doublet lens cap- 
able of being used alone or in combination with 
other lenses, as in the casket lenses (which see). 


CONVEX LENS 
A lens that is raised in the middle; the oppo- 
site to concave. The ‘‘ convexo-convex”’ has 


A. Convexo- 5B. Convexo- C. Convexo- 
convex Lens concave Lens. plane Lens 
two convex surfaces, as at A; the “ convexo- 
concave,” one surface of each kind, as at B 


141 


Copper 


(identical with the ‘“‘concavo-convex” and 
“‘meniscus’’); and the “‘convexo-plane,’’ one 
convex and one plane surface, as at C. The 
“biconvex’’ lens is the convexo-convex. 


COOLING CHAMBER (Fr., Chambre réfrigér- 
ante ; Ger., Ktuhizimmer) 

An atrangement employed in dry-plate manu- 
factories for cooling the emulsion on the plates 
and causing it to set as quickly as possible. It 
may consist of a fennel ihaged compartment 
about 15 ft. long, open only at each end, and 
furnished with an ice tank at the top, while 
below is a cold slab resting on a metal tray 
filled with ice water. The plates on coming 
from the coating machine are received on an 
endless travelling band of woven wire, by 
which they are carried along the cold slab and 
through the cooling chamber, emerging with the 
emulsion sufficiently set to allow them to be 
removed. 


COOPER-HEWITT LAMP (See “ Mercury 
Vapour Lamp.’’) 


COOPER’S PROCESS 

A plain, salted paper printing process now 
practically obsolete. The paper was sized 
with an alcoholic solution of resin, the silver 
sensitising solution being afterwards applied. 
More simple sizing solutions are now used, as 
described under the heading, “Plain Paper 
Printing.” 
COPAL VARNISH (Fr., Vernis copal; Ger., 

Kopaifirnis) 


Gum copal is a natural product, which is 
described under the heading “Gums and 


Resins.”’ Copal varnish is sometimes employed 
for photographic purposes, a good formula 
being :— 

Copal . : . ag 2, OZ, — Y10° g, 

Oil of turpentine . eT os 375 CS. 

Linseed oil . : pk Rees 1 eer 


But as such a varnish cannot properly be 
made by the cold process, and as the heating 
of oil and turpentine is attended by grave risk 
of fire, it is better to buy the varnish ready 
made, advice which applies to all oil varnishes. 


COPPER (Fr., Cuivre; Ger., Kupfer) 

Copper has become a most important and 
almost universally used metal for photo-engrav- 
ing. It began to supersede zinc, which was 
formerly used, as soon as the fish-glue enamel 
process came into vogue, it having been found 
that zinc deteriorated in the “ burning-in ” pro- 
cess to which the enamel was subjected. The 
copper used is mainly of American origin, and 
this kind is considered the best for the purpose ; 
a considerable amount also comes from the Con- 
tinent, but this is generally harder, more brittle, 
and more difficult to etch. The copper comes 
on to the market in well-rolled and finely- 
polished sheets of eitier 16 or 18 B.W. gauge 
(065 in. or -049 in.; the higher the gauge 
number the thinner the metal). Copper is 
invariably etched with ferric chloride solution 
of a strength of 35° to 40° Beaumé (sp. g. up 
to 1°36). 


Copper Acetate 


COPPER ACETATE (Fr., Acétate de cutore ; 
Ger., Kupferacetat) 

Synonyms, copper subacetate, verdigris. 
Cu(C,H30,), H,O. Molecular weight, 199°5. 
Solubilities, 1 in 14 water, soluble in alcohol. It 
should be kept well stoppered. It is a poison, 
the antidotes being emetics and the use of a 
stomach pump, then white of egg, charcoal, iron 
filings, magnesia, or pure potassium ferrocyanide ; 
avoid milk and fatty acids. It takes the form 
of bluish-green crystals, obtained by dissolving 
copper carbonate in acetic acid. It is used as a 
colour screen in sensitometry. (See ‘“ Colour 
Sensitometry.’’) 


COPPER AND AMMONIUM SULPHATE 
(Fr., Ammonio-sulfate de cuivre; Ger., 
Kupferammonitumsulfat) 

Synonyms, ammonio-cupric sulphate, ammo- 
nio-sulphate of copper. CuSO, 4NH, H,0. 
Molecular weight, 245:5. Soluble in water. 
It is a poison; for the antidotes, see under 
the heading ‘‘Copper Acetate.” It is in 
the form of a dark-blue crystalline powder, 
and is obtained by dissolving copper sulphate 
in a solution of ammonia and precipitating by 
alcohol. 
metry, and is then prepared in solution as 
follows :— 


Copper sulphate . <i EAR: Bite eae. 
Distilled water I5 OZ 750 CCS, 


Dissolve, and add enough liquor ammoniz (-880) 
to redissolve the precipitate first formed and 
give a deep blue clear solution. Filter, and 
add— 


Distilled water to . . I,00O ccs. 


COPPER BROMIDE (Fr., Bromuve de cutore; 
Ger., Kupferbromid) 


Synonym, cupric bromide. CuBr,. Molecular 
weight, 223°5. Solubilities, very soluble in water, 
less so in alcohol. It occurs as a greyish black 
crystalline powder, but it is most easily made by 
double decomposition, as follows :— 


20 OZ. 


A. Copper sulphate . 250 grs. 29 g. 
Hot water . iG OZ. 500 ccs. 

B, Potassium bromide. 238 grs 27°6 g. 
Distilled water IO OZ. 500 ccs, 
Mix the solutions and allow to cool. It has-been 


suggested. for use in the intensification of nega- 
tives and for bleaching bromide prints for subse- 
quent sulphide toning. 

In process work, the copper bromide intensifier 
is employed for intensifying half-tone negatives, 
chiefly for the reason that it is more amenable to 
the “cutting” or reduction which every nega- 
oo has to undergo in order to sharpen up the 

ots, 

The following is the formula generally em- 
ployed for making up the copper bromide 
solution :— 


No. 1— 
A. Potassium bromide 500 gts. 52 g. 
Water . : : IO Oz, 500 ccs, 
B. Copper sulphate . 500 gts. 52 g. 
Water . i i IO oz. 500 ccs. 


Dissolve A and B separately and mix together, 
allowing to stand twelve hours before using. 


142 


It is used as a light filter in sensito-. 


Copper, Intensification with 


The negative is bleached in this solution, rinsed 
well, and placed until blackened in solution 


No. 2— 
Silver nitrate . A I OZ. 55 &. 
Nitric acid : +. 40, mins, 4 ccs, 
Distilled water to . 20 oz. 1,000 ,, 


Greater density is given by flowing over a solu- 
tion of either ammonium or sodium sulphide. 
The copper bromide intensifier is usually em- 
ployed in conjunction with the cutting or reduc- 
ing solutions of iodine and cyanide. | 


COPPER CHLORIDE (Fr., Chlorure de cuivre; 
Ger., Kupferchloria) 

Synonyms, cupric chloride, copper bi- or di- 
chloride. CuCl, 2H,O. Molecular weight, 170-5. 
Solubilities, 1 in -83 water, very soluble in alcohol 
and ether. It is deliquescent, and must be kept 
in well-stoppered bottles. It is a poison; for 
antidotes, see “‘ Copper Acetate.” It takes the 
form of a greenish crystalline mass, obtained by 
dissolving copper carbonate in hydrochloric 
acid, or in a similar manner to the bromide, 
using 117 grs. of common salt in B solution. 
It is occasionally used as a reducer, Spiller’s for- 
mula being :—(1) Alum, 2 0z.; copper sulphate, 
2.0z.; Salt, 40z.; and water, 200z. (2) Saturated. 
solution of common salt. Mix equal parts of 1 
and 2, immerse negative, and wash. 

Also, it has been suggested as an addition to 
printing out emulsions to increase contrast, and 
was used in Obernetter’s process (which see). 


COPPER, INTENSIFICATION WITH 

A process for intensifying gelatine negatives. 
A solution of bromo-iodide of copper is prepared 
as follows :— . 


Copper sulphate - roo ge. 76m. 
Water : . 3 OZ. 1,000 ccs, 


When dissolved, add with constant stirring the 
following, which must also be dissolved :— 


Potassium iodide ° 8 gts. 18:2 g. 
Potassium bromide . 20 ,, 45°6,, 
Water : ° I OZ. 1,000 ccs, 
A slight precipitate of iodide of per of a 
deep yellow colour forms; this is allowed to 


settle and the clear part poured off for use. The 
fixed and washed negative is placed in the above 
until bleached and of a canary-yellow colour, 
from five to fifteen minutes being usually 
required. The solution may be used repeatedly 
if strengthened occasionally with a few drops of 
a mixture made by dissolving 12 grs. of iodide 
and 36 grs. of bromide in 2} oz. of water. After 
bleaching, the negative is washed well, and dark- 
ened by placing in a strong solution of sodium 
sulphite to which a few grains of silver nitrate 
are added. Good results may also be obtained 
by darkening with a hydroquinone developer. 
The colour of the resulting negative is strongly 
affected by the solution used for darkening 
after bleaching. The above usually gives a 
reddish deposit which is very non-actinic; 
rodinal a brown image, and the sulphite-silver a 
darker one. Variations in colour when hydro- 
quinone is used may also be obtained by altering 
the proportions of sulphite and hydroquinone 


Copper Ferricyanide 


Both the bleaching and the darkening must be 
done in daylight; the stronger the light the better 
and quicker the results. After darkening, the 
intensified negative is well washed in water and 
finally dried. The process may also be used for 
slides and bromide paper. When used for prints, 
the paper turns blue when bleaching, owing to 
the formation of iodide of starch, but the colour 
disappears when the hydroquinone is applied, 
Sis the colour of the print is usually a good 
rown. 


COPPER AND POTASSIUM  FERRI- 
CYANIDE (Fr., Ferricyanure de cuivre et 
de potassium ; Ger., Kupfer-Blutlaugensalz) 

KCuFe(CN),. Molecular weight, 314°5. 

Soluble in water, It is poisonous; for antidotes, 

see “Copper Acetate.” This salt is always 

prepared in solution by double decomposition, 
generally in the presence of an alkaline citrate. 

It is used for toning bromide prints and trans- 

parencies (see “Copper Toning’’), and is then 

reduced to the double ferrocyanide, K,CuFe 

(CN), (a brownish-red powder insoluble in 

water), by the metallic silver; white silver ferro- 

cyanide is also formed. 


COPPER PRINTING PROCESS 

A printing process introduced by Obernetter, 
based on the fact that copper forms with chlorine 
a green salt (copper chloride) soluble in water. 
This salt is sensitive to light, which reduces it to 
hypochloride of copper. Paper is saturated 
with a mixture of copper chloride and iron 
chloride, and when dry is exposed to light under 
a negative. Afterwards it is immersed in a 
solution of potassium sulphocyanide, and ulti- 
mately treated with red prussiate of potash, a 
brown picture being the result. 


COPPER REDUCER FOR BROMIDES 
_ & process of locally reducing over-dense 
bromide prints, introduced by Fourtier in 1905. 
A 5 per cent. solution of copper sulphate is mixed 
with enough solution of potassium carbonate 
until no further precipitate is formed. The pre- 
cipitate is collected on a filter paper and washed 
with several changes of water, and then dissolved 
in water to which a few drops of hydrochloric 
acid have been added. To this clear solution a 
strong solution of ammonia is added until 
the precipitate first formed is re-dissolved, the 
resulting rich-blue liquid being a solution of 
ammonio-chloride of copper. The actual re- 


ducer is :— 
Copper solution (as 
above) . : a On 25 ccs. 
“Hypo” solution (5%). 4 5, 25 5, 


Water . 20 » 


The prints should be well soaked in water, 
laid face upwards on a sheet of glass or the 
bottom of a clean porcelain dish, and the reducer 
applied with a tuft of cotton-wool. The action 
of the reducer is stopped by washing the print 
in water, and the reducer made to work more or 
less rapidly by varying the quantity of water. 
The above is really a roundabout method of 
making copper chloride, and the same purpose 
is served by mixing solutions of copper sulphate 
and common salt. 


I,000 4 


143 


Copperas 


COPPER SULPHATE (Fr., Sulfate de cutore ; 
Ger., Kupfersulfat) 


Synonyms, cupric sulphate, blue vitriol. 
CuSO, 5H,O. Molecular weight, 249°5. Solu- 
bilities, 1 in 2°5 water, 1 in 400 alcohol. It is 


efflorescent, and should be kept well stoppered. 
It is a poison; for antidotes, see ‘“‘ Copper 
Acetate.” Large deep blue crystals, obtained by 
dissolving copper carbonate in sulphuric acid. 
It was occasionally used in the developer for 
wet collodion, and is now used chiefly for making 
the bromide, chloride, and ferricyanide salts. 
It forms a rich blue solution with excess of liquor 
ammoniz, and is a useful filter for colour sensito- 
metry and three-colour work. 

In process work, copper sulphate is used as 
an addition to the wet-plate developer. Its 
action is said to be merely that of retarding the 
oxidation of the ferrous sulphate. Copper sul- 
phate is also employed by process workers in 
the copper bromide intensifier. In electrotyping 
it is the salt used with sulphuric acid to form the 
depositing solution, 


COPPER TONING 

A process for toning bromide prints, originally 
introduced by Eder and Toth in 1876, and 
modified by Namias and others. The following 
method, introduced by W. B. Ferguson in 1900, is 
the most satisfactory. The colours obtained 
range from warm black, reddish sepia, brown, 
purple brown, purple crimson, reddish purple, 
through many shades of red to the so-called red 
chalk, according to the quality of the print and 
duration of toning. The Ferguson formula has 
appeared in many forms, a popular one being :— 


A. Coppersulphate . 60 grs. 6 g. 
Potassium citrate 240 ,, pe 
Water to . 20 OZ. 1,000 ccs, 

B. Potassium  ferri- 

cyanide . .  3Of gem 5 g. 
Potassium citrate 240 ,, "ee 
Water to 20 OZ. 1,000 ccs. 


Use equal parts of each and immerse the print 
until the desired shade is obtained. The toning 
is made more rapid by adding 5 grs. of citric 
acid per ounce of toner. Used in its normal 
state the bath produces the first tones very 
rapidly, while the final colour (red) requires from 
twenty to forty minutes, according to the quality 
of the print. Washing for ten minutes only is 
necessary to stop the action of the toner at any 
desired stage. The colours are produced by 
the formation of copper and silver ferrocyanides. 
The following copper bath has also been 
recommended for rich red tones :— 


Ammonium carbonate 


(saturated solution) oz 1,000 ccs, 
Copper sulphate » 4 3Orgrs 2 g. 
Potassium ferricyanide 25 ,, oe 


Owing to the alkaline condition of this bath it 
ptoduces red tones more quickly than does 
the Ferguson formula. 


COPPERAS 

A common name for various sulphates. Thus, 
copper sulphate = blue copperas ; iron sulphate 
= green copperas; zinc sulphate = white 
copperas. 


Coppering Solution 


COPPERING SOLUTION 

A superficial coating of copper may be applied 
to etched zinc plates by neutralising copper 
sulphate with a strong alkali, such as ammonia 
or cyanide. Previously, the plate is well washed 
and scrubbed with caustic potash and whiting, 
and is then immersed in the solution for a few 
minutes, when it will be found coated with a 
sufficient covering of copper. 


COPYING 

Copying should present no serious difficulty 
provided suitable precautions are taken, and 
cotrect exposures given. It is essential that 
the print to be copied should be held perfectly 
flat on a board which is parallel with the sensi- 
tive plate. If this condition is not observed, a dis- 
torted image will result. The arrangement shown 
at A (p. 145) is simple, inexpensive, and answers 
well for copying and also for other photographic 
work. The direction of lighting is important. 
A direct front light minimises the effect of the 
grain of the paper, while a strong side light 
accentuates it. On the other hand, a direct 
front lighting cannot be adopted for glossy 
sutfaced prints on account of the reflections. 
To avoid the sheen of the glossy surface, 
lighting from one side, slightly in front, is 
necessary. 

For copying pictures under glass, the camera 
front should be covered with a black cloth, and 
a black or dark cloth should be hung up close 
behind the camera to avoid reflections. A side 
lighting is desirable for the same reason; but 
where the original is liable to show a grain, the 
lighting should be from two sides. (For copying 
oil paintings or water-colour drawings, sce 
** Paintings, Photographing.”’) 

For copying an ordinary silver print, or any 
strong photographic print with a glossy surface, 
a rapid plate will give the most truthful rendering 
of the gradation. If the print is faded or yellow 
an isochromatic plate should be used. For 
copying a line engraving or drawing, or a wash 
drawing, or a photographic print with very little 
contrast on matt-surfaced paper, a. slow plate 
specially made for copying, such as a “ process” 
plate or a fine grain ordinary plate, will give 
the most satisfactory negative. In all cases the 
plates should be backed. Correct exposure is 
most important, and the best method of deter- 
mining this is by using a meter, which should be 
placed flat against the picture that is being 
copied and the time that is required for matching 
the standard tint noted. Using a plate of which 
the speed is 200 H. & D., the exposure for copying 
a glossy silver print the full size of the original, 
and using the aperture marked //16 on the 
diaphragm scale, will be from one-fourth to one- 
half the meter tint if a Wynne meter is used, 
and from one-eighth to one-fourth with a Watkins 
meter. A dark or red-toned photograph will 
require longer exposure than a light or cold- 
toned print. For copying a line drawing, one- 
half the meter tint for a Wynne meter, and one- 
fourth for a Watkins will be the correct exposure 
for a slow plate, 40 H.& D. For a black-and- 
white drawing in wash, these exposures should 
be doubled. 

The above exposures are for making a copy the 
same size as the original. For other proportions, 


I44 


Copying Illustrations 


the following will be the relative exposures, the 
lens aperture being the same throughout :— 


Times the 
scale of the Relative 
original exposure 
Enlarged to . as 2 iis 2} 
ha AAS - ‘It ae 14 
Copying same size I se Bi 
Reduced to ; # a 2 
ne ee : % ys 2 
” ” - Le $ “* 1s 
” ” ° ° 4 os 13 
»” 99 e t ~ $ 


In process work, the art of copying has been 
brought to great perfection for photo-mechanical 
processes, where the reproduction has generally 
to be made from a print or drawing. The essen- 
tials that are carefully studied are: The light- 
ing of the subject ; the parallelism of the original 
to the sensitive surface; the sharpness in defini- 
tion of the image ; and the opacity and clearness 
of the respective parts of the negative. The 
first condition is generally secured by electric 
arc illumination. The second is secured by the 
use of stands on which are rails, the camera and 
copyboard running on these rails to and from each 
other; also by rigid and accurate construction 
of the camera. The third is secured by the 
choice of suitable lenses such as are specially 
made for process reproduction. The fourth is 
secured by the adoption of suitable plates or 
processes, the wet collodion process being gener- 
ally considered the best for such work. Further, 
it is very important to avoid vibration (sce 
“Copying Stand”’). 


COPYING ILLUSTRATIONS FOR TRANS- 
LATION INTO LINE DRAWINGS 

A modification of the arrangement that is 
illustrated and described under the heading 
“Camera, Vertical’? may be used for project- 


Arrangement for Projecting Illustrations for 
Translation into Line Drawings 


ing book or newspaper illustrations, when 
such illustrations are taken from photographs 
and have to be translated into line. The 


AHdVUDOLOHd AdVOSGNYV'I 
Sd WA ‘NOLONITIFTM “d “A ‘f AD NOWWOD XAAISIM NO 


Copying Stand 145 


glass platform a (see the illustration to the 
present article) is covered with a drawing-board, 
and upon this is placed the paper, etc., upon 
which the sketch is to be made. A trans- 
parency made from the illustration to be copied 
is placed in the lantern B, and by means of a 
sloping mirror c attached to the lantern lens 
hood an image of the illustration is projected 
upon A, where it can be drawn on the paper 
provided. 


COPYING STAND (Fr., Pied-table, Chevalet de 
veproduction ; Ger., Reproductren-Stativ, 
Kopier-Stativ) 

An arrangement for keeping the camera and 
copy parallel when reproducing plans, drawings, 
photographic prints, etc. It usually consists of 
an upright copyboard or easel running on 
parallel rails, and capable of being clamped in 
any position. The camera may also be mounted 
to run on the rails, but is often stationary. Illus- 
tration A shows an ordinary copying stand. 

In process work, the copying stands used are 
the products of considerable ingenuity, the 
occasion for which was the necessity of avoiding 
any want of sharpness through vibration. One 


py 1) 7, 
er Mh 
Hi yj) 


of the earliest and most usual methods for attain- 
ing this object was to suspend the copying base 
on ropes which depend from the ceiling; but 
the ropes get hardened by constant tension and 
in time fail to neutralise the vibration. One 
way of overcoming this drawback was to insert 
spiral springs between the ends of the ropes and 

e suspension hooks; and another was to 
pi gt the base from a beam swinging like a 
scale beam. 


The above methods are now considered clumsy 
and obsolete, and the usual form of apparatus 
now employed is the spring stand B. The base 
is swung on spiral springs F attached to a rigid 
stand. Where no vibration is anticipated, rails 
may be laid on the floor and the camera and 
copyboard placed on separate stands, with 
wheels running directly on the rails, or the copy- 
board may be fixed to the wall whilst the camera 
is on a running carriage. This system is largely 
used in Government offices for map reproduction. 

Another plan often employed for large work 
is to have rails laid both inside and outside the 
dark-room, the copyboard being on a carriage 
outside, and a plate-holder being mounted on a 
catriage inside, whilst the lens is fixed in an 
opening made in the wall of the dark-room; 
in this way the dark-room itself becomes the 
camera. Where daylight is used for illumin- 

10 


Copying Stand 


ation, tilting stands are sometimes employed 
in order to get the best light possible on the 
original. 

A curious form of copying apparatus used for 


een 


B. Spring Copying Stand 


copying large paintings in the open air is the 
revolving camera stand, which can be turned 
according to the direction of the sun’s rays. 

The vertical copying stand C is often used for 
copying from books, or from small natural objects 
which can be best arranged on a horizontal 
board. Levy’s copying stand D and E combines 
not only the vertical, but also the tilting and 
horizontal forms. With these vertical stands a 
prism or mirror box must be used in conjunction 
with the lens. 


SAAANWAC AMAA RE) ANS: 


NW 
V 


EN 


Wl 


Coa 


C. Vertical Copying Stand 


For producing reversed negatives, which 
invariably have to be made for photo-mechanical 
processes, the camera stands must be provided 
with a turntable so as to place the camera side- 


Copyright 


ways to the copyboard, the image being then 
reflected by mirror or prism, as shown in the 
vertical stand C. On the Continent, copying 
stands have been made for such reversal work 
with the copyboard and the camera carriage both 
placed across the stand at an angle of 45 degrees, 
but, of course, still parallel to one another and 
provided with reversing prism as before. In 
this way some floor space is saved with large 
cameras. 

For copying transparencies a “‘ transparency 
attachment”? is usually connected up to the 
camera and stand; it is a simple light-tight 
conical bellows with provision for inserting the 
transparency. Rotary copyboards and rotary 
transparency holders are often employed in 
copying, especially in colour work, to place the 
megative at different angles from the vertical or 


/ AY CM “Of 


= 


146 


Copyright 


the term “colourable imitation.” In other 
words, a copy need not be an exact copy. It is 
sufficient to be able to show in the case of the 
infringement of a copyright that the original 
photograph has been copied by a mechanical 
or hand method. 

The period of protection granted by the Act 
is for the term of the natural life of the author 
and seven years after his death. It has no 
relation to the life of the owner of the copyright 
except in the case where he is also the author. 
Usually, there is no room for doubt as to who 
is actually the author, but in the case of a photo- 
graphic firm, where the finished photograph 
passes through a number of hands, it has been 
held that the author is the person who effectively 
is as near as he can be the cause of the picture 
which is produced—that is, the person who 


SS 
lea Les so 


Kd i 
7 io 5 
we b 
di 
p i 
WW) 
“* iy a 
t i 
4 2 . 
\ 1 
ee 
‘} i ‘ 
4 
i 
b 


D and E. Combination Copying Stand 


horizontal line. For correcting distortion a 
transparency holder with universal movement 
may be employed. 


COPYRIGHT (Fr., Dyvrott d'auteur ; 
Verlagsrecht, Urheberrecht) 


Protection against copying and other forms 
of reproduction is granted to photographs 
equally with paintings and drawings. The Act 
by which this protection is afforded is the Copy- 
right Works of Art Act of 1862, the clauses of 
which Act, taken in conjunction with the judg- 
ments. of the courts during the years that have 
intervened since then, cover the many incidents 
which may arise in the creation of copyright, in 
its assignment, and in the infringement of copy- 
right works. ‘The Act defines copyright as “ the 
sole and exclusive right of copying, engraving, 
reproducing, and multiplying any photograph 
and the negative thereof by any means and of 
any size ’’—that is to say, the reproduction of a 
photograph by another graphic method, such as 
drawing or painting, may yet be an infringement 
of the copyright. The Act in another place uses 


Ger., 


superintended the arrangements by putting the 
people into position. It has also been held that 
an absentee principal cannot be the author, even 
though, by the creation of system in his business, 
he may be actually just as responsible for the 
result as though he had been present. 

The most important clause in the Copyright 
Act is that which describes the conditions as to 
payment when a photograph is taken, because 
upon these conditions the ownership of the 
copyright depends. The Act expressly states 
that when the negative of any photograph is 
made for or on behalf of any other person “ for 
a good and valuable consideration,” the copy- 
right belongs to the person for or on whose 
behalf the work is done. Thus, in the case of 
an ordinary sitter in a studio, the copyright is 
his; in the case of a landscape photographer 
working for an employer, all copyrights in the 
views taken are the employer’s. The question 
of what is “‘ good and valuable consideration ” 
has involved some nice points of law. Articles 
of value, or board and lodging, may be agreed 
upon as “valuable consideration,’ and there 


Copyright 


is, in fact, one case in which the granting of 

ermission to photograph certain premises was 
judged to be “ valuable consideration ’’ to the 
photographer because it gave him the oppor- 
tunity to sell numerous copies of the photographs 
he had taken. 

It should be noted that the Act does not say 
on payment of the consideration, and, so far as 
the ownership of copyright is concerned, non- 
payment to the photographer by his custon:er, 
or employer, does not give the first-named any 
rights in the photographs; the copyright remains 
with the customer or employer, whilst the photo- 
grapher must sue in the usual course for payment 
or wages, 
ship of a copyright this forms a useful test. If 
one is in a position to sue for payment one 
cannot then have any ownership in the copy- 
right. 

The portrait photographer should also note 
that in the case of negatives taken at the same 
time as others at the sitting, but not ordered 
by the customer, the copyright is neverthe- 
less the property of the customer. In cases 
where this point has arisen it has been held that 
payment was for the labour of the artist as a 
whole, and, therefore, covered all the exposures 
made at the sitting. Any use made of such 
extra negatives will thus be an infringement of 
the sitter’s rights. 

Again, when, as sometimes happens, the por- 
trait of a person is taken by the order and at 
the expense of a second person, the copyright 
naturally becomes the property of the person 
paying, or suable for payment. And, in the 
absence of any agreement that the photo- 
grapher should make some negatives for himself 
at such a sitting, the whole of the portraits 
taken are the property of the person ordering 
the work. 

Though the Copyright Act does not say any- 
thing about the ownership of the negative, it is 
perfectly clear on one point—namely, that the 
sale or disposal of the negative by the owner of 
the copyright to another person without the 
formal assignment of the copyright in writing to 
either buyer or seller causes the copyright to be 
destroyed. This fact should be borne in mind 
when purchasing negatives or acquiring them 
along with the purchase of a business. It is 
necessary to draw up an itemised list of the 
subjects, sufficient for separate identification, 
and to have the whole document signed by the 
vendor transferring the copyright to the pur- 
chaser, or by the purchaser reserving the copy- 
tight to the vendor, according as the copyrights 
ate, or are not, to change hands. 

Before referring to the assignment and regis- 
tration of copyright, one minor clause of the Act 
must be noted—namely, that which enacts 
that any person may copy any work in which 
there is no copyright, and may represent any 
scene or object, notwithstanding that there 
may be copyright in other representations of 
such scene or object. This clause has a very 
practical application in the reproduction of the 
works of Old Masters, in which, of course, there 
is no copyright, but any number of photographers 
may make copies of such works and severally 
acquire rights in their copies, even though these 
latter are practically identical. Similarly, there 


In cases of doubt as to the owner- | 


147 Copyright 


is nothing to prevent several photographers from 
photographing a landscape from a particular 
point of view; even though the negatives are 
almost identical, copyright may be obtained by 
each separate author. 

Assignment of the copyright in a photograph 
may be whole or partial. The sole rights to 
reproduce in any form or place whatever may 
be sold with, or without, the negative, though 
there can be no object in the photographer retain- 
ing the negative, since his rights to make a 
single print from it have been disposed of. It 
is more usual, however, to assign specifically 
limited rights to reproduce, such as in a given 
issue of a journal or newspaper, as a calendar 
or window-bill, as a postcard, or as an advertise- 
ment for a particular classof goods. The nature 
of the assignment being clearly defined, the 
photographer is left free to dispose of other 
limited assignments in other ways, but a form 
of assignment loosely worded (for instance, the 
following: ‘“‘ Received of A. B. tos. 6d. for the 
right to reproduce my photograph of Trafalgar 
Square.—C. D.’”’) might be taken to mean the 
sole rights of reproduction. An assignment or 
licence to reproduce should clearly state the 
particular purpose for which the photograph is 
to be used. In the case of reproduction in news- 
papers, it is usually understood that the photo- 
grapher’s name should be acknowledged under 
the photograph, or on the same page, and that 
no use be made of the photograph without extra 
payment in extra issues of the paper, or any 
other publication of the same proprietorship. 

Although anyone purchasing the sole copy- 
right in a photograph or other work is thereby 
at liberty to reproduce it in any form, the Act 
forbids the alteration of such photograph, or 
the reproduction thereof in an altered form, 
during the life of the author and without his 
consent—that is to say, that such altered version 
must not be represented as the unmodified work 
of the originator. 

The registration of a copyright is important 
to those who have business in selling rights of 
reproduction, inasmuch as the Act provides that 
*‘no proprietor of any such copyright shall be 
entitled to the benefit of the Act until such 
registration, and no action shall be sustainable, 
nor any penalty recoverable, in respect of any- 
thing done before registration.’’ In other words, 
registration is a formal claim to rights in the 
photograph. It is made at Stationers’ Hall, on 
forms provided for the purpose. On this form 
five columns are provided, but it is only neces- 
saty, when registering a copyright, to make 
entries in Nos. 1, 4, and 5; Nos. 2 and 3 are 
required only when a copyright is assigned by 
one person to another. In column 1 a short 
description identifying the photograph is given, 
in No. 4 the name and address of the proprietor 
of the copyright, and in No. 5 the name and 
address of the author. The author, as already 
pointed out, may or may not be the same person 
as the proprietor. This form, filled up on these 
lines, is deposited at Stationers’ Hall, together 
with a copy of the photograph, the fee for 
registration being one shilling. The precise form 
of the photograph is immaterial ; a straight print 
from the negative suffices to protect the photo- 
grapher’s rights regarding the issue of enlarge- 


Copyright 


ments or even of worked-up reproductions in 
colour by hand or by three-colour printing. It 
is simply necessary that the photograph regis- 
tered should plainly identify the original work 
of the author. 

Infringement of copyright may take a number 
offorms. The Act specifically forbids any person 
to “‘repeat, copy, colourably imitate, or other- 
wise multiply for sale, hire, or distribution,” 
or to cause or procure these acts to be done. 
The phrase “ colourably imitate’ protects the 
photographer against piracy of his work by 
draughtsmen or artists, who might use the 
photograph as a basis for drawings; it is not 
necessary, to prove infringement, that the illegal 
copy should be identical with the original from 
which it was made. 

The Act distinguishes between two classes of 
infringer: (1) those who in knowledge or ignor- 
ance commit one of the acts mentioned above, 
and (2) those who, with knowledge of the 
unlawful character of the copies, import orf 
distribute the latter in the United Kingdom. 
The copyist, or person who employs a copyist, 
is regarded as liable whether he act in knowledge 
or ignorance of the copyright, whereas an 
importer is liable only when he acts with know- 
ledge of the unlawful nature of the copies. It 
will thus be seen that a photographic enlarger, 
who prepares an enlargement of a photograph 
sent to him, is equally liable with the person 
who gave him the order, and this even though 
both may be in ignorance of the existence of 
any copyright. Under the Copyright Act there 
is no need that a photograph which has been 
registered at Stationers’ Hall should be marked 
“copyright,” but it isa natural assumption that 
any recent photograph is copyright, even though 
formal claim (registration) has not been made. 

The remedies for unlawful copying granted 
by the Act are of two kinds: (a) penalties and 
(b) damages. As already stated, no penalty 
can be recovered for any such infringement 
committed before the copyright has been regis- 
tered, but damages may be obtained in the case 
of copies which are made before registration and 
sold afterwards. The maximum penalty which 
can be obtained under the Act is £10 for each 
unlawful copy, together with the forfeiture by 
the infringing party to the proprietor of the 
copyright of all such copies. Formerly, this 
provision of the Act was interpreted to mean a 
payment of a coin of the realm for each unlawful 
copy, and on this basis large sums were form- 
etly obtained in the case of unlawful reproduction 
in a newspaper of large edition. But a later 
judgment of the Court of Appeal has held that 
it is not necessary to fix the total penalty at a 
sum which, when divided by the number of 
copies, works out to a coin of the realm. When 
taking action for penalties it is only necessary 
to prove the infringement. The photographer 
must show that the copyright is his property by 
virtue of the fact that he took the photograph 
without payment in the original instance, or 
that it was assigned to him in writing at the 
time of taking, or that he had subsequently 
purchased it. In action for recovery of damages 
he must prove not only his ownership of the 
copytight, but the damage sustained by the 
infringement. 


148 Corona Photography 


Where a registered photograph has beet 
reproduced without permission, it is an easy 
matter to obtain satisfaction from the offending 
patty, but when the photograph has not been 
registered the owner of the copyright needs to 
proceed with some care. He should first register 
the photograph immediately, and he is then in 
a position to take such action against the parties 
still producing, or those selling, the copies as 
wili induce the infringer to settle the matter 
privately. Very frequently the infringement is 
the result of ignorance or carelessness, and it is 
usually good practice to assume that it is so, 
and to write pointing out the infringement and 
to ask what the party in question is prepared 
to do. In this letter it is not wise to name any 
specific sum which would be acceptable to the 
photographer. Where the infringement is 
clearly unintentional, many photographers are 
prepared to accept twice (or even the same) the fee 
payable had application for the use of the photo- 
gtaph been made by the publisher. 

Copyright, created and registered in England, 
is secured ipso facto in the other countries sub- 
scribing to the Berne Convention of International 
Copyright. These countries are as follow: 
Algiers, Belgium, Denmark and the Faroe 
Islands, France and its colonies, German 
Empire, Hayti, Italy, Japan, Liberia, Luxem- 
burg, Monaco, Norway, Spain, Switzerland, 
Tunis. Under this Convention the photo- 
grapher in each country must comply with the 
formalities of his country (the country of origin), 
and he obtains in the other countries the degree 
of protection which is granted to natives in 
these countries. The degree of protection varies 
within wide limits among civilised countries. 
In France, for example, protection is granted 
only to such photographs which are adjudicated. 
to be works of art, and it would appear that 
judgment in this respect must be given in regard 
to each particular photograph, apart from the 
reputation of the photographer as an artist. 
In some countries—Germany and Belgium, for 
example—it is not necessary to register, and 
therefore it is difficult to discover whether the 
formalities in the country of origin have been 
complied with in these cases. In Great Britain 
—and, indeed, whenever there is any doubt 
—the safest course is to assume that copy- 
right exists in any photograph, painting, or 
drawing. : Go. B. 


CORALLIN (Fr., Coralline; Ger., Corallin) 
Synonyms, peonine, aurin. A mixture of 
several complex aniline dyes, which is interest- 
ing as being the first dye used to colour-sensitise 
collodion films. It is not used now, having am 
extremely weak action on gelatine plates. 


CORONA PHOTOGRAPHY 

The corona is the brilliant pearly-white lumin- 
escence observed round the eclipsed sun during 
a total solar eclipse, when the ordinary brilliant 
sunlight is obscured by the intervention of the 
dark moon. Many attempts have been made by 
astronomers to observe it visually or to photo- 
graph it in ordinary sunlight, but all these have 
hitherto been unsuccessful, and it is only during 
an eclipse that it can be examined. There is no 
limit, either of size or quality, to the apparatus. 


Corona Photography 


which can be usefully employed to photograph 
this wonderful solar appendage, and as indicat- 
ing what are perhaps extremes, excellent pic- 
tures of the coronal streamers have been made 
with ordinary camera lenses of about 5 in. focal 
length, and also with large mirror telescopes of 
more than 70 ft. focal length. Each variety, 
however, has its special advantages, and the 
general apparatus may be divided into two divi- 
sions according to the scale on which the pic- 
tures are ptimarily photographed. With the 
small scale cameras, lenses of very great angular 
aperture can be employed, with all the advan- 
tages of extensive flat field and light intensity. 
These will be most useful for recording the 
extreme limits of the coronal streamers or rays, 
which are found to be very different from eclipse 
to eclipse, so that as complete a record as pos- 
sible is desirable. 

With the large scale apparatus the programme 
is best confined to obtaining detailed pictures of 
the brighter regions of the corona near to the 
sun’s disk, and as the light gradations in this 
region are very great, it is generally found neces- 
sary to take exposures of different lengths for 
the different zones, and develop accordingly, 
so that the intense portions are not rendered 
unprintable. 

If possible, the most rapid panchromatic 
plates should be employed for photographing the 
corona, as the principal part of the corona 
radiations is in the green near wave length 5,303. 

The exposures possible will, of course, depend 
on whether the observer has the use of an equa- 
torial mounting and driving mechanism or not. 
If he has not, probably half a second will be the 
maximum exposure possible with a camera of 
about 7 in. to 9 in. focal length. When the 
more elaborate mounting is available, exposures 
of from ten seconds to four or five minutes 
ate given so as to record the farthest outlying 
streamers. 

Very interesting series of experiments have 
been tried at several eclipses. For comparison 
purposes two exactly similar photographic 
cameras have been used side by side, clamped 
firmly together so as to move as one. In front 
of one of these cameras, between the lens and the 
corona, there has been placed a special piece of 
apparatus for detecting polarised light, so that 
if any of the light coming from the solar corona 
is polarised in any particular direction, the differ- 
ence will be clearly shown on the photograph 
by the presence of a series of bands as compared 
with the image taken with the other camera 
having the lens alone. By such means it has been 
satisfactorily proved that a large proportion of 
the light from the corona is polarised, and it is 
thought that this may be owing to its being 
light from the sun reflected from the minute 
particles of which the corona is assumed to be 
composed. 

By obtaining comparable photographs with the 
same instruments at intervals during a long 
period of years it has been noticed that the form 
of the corona decidedly changes; and these 
changes are found to be in accord with the 
changes on the sun’s surface as evidenced by 
the presence or absence of the dark irregular 
markings called sunspots. When these are very 
numerous, showing the sun to be very active, 


149 


Cosmical Photography 


then the corona is found to be very extensive 
in all directions round the sun, long streamers 
passing off practically in all directions. When, 
on the contrary, the sun’s activity is at a 
minimum, and there are few sunspots, then 
the coronal streamers are chiefly confined’ 
to the regions on either side of the sun’s 
equator; the regions near the sun’s poles 
are at these times occupied by very beau- 
tiful plumes or aigrettes, which have all the 
appearance of the stream lines shown by a series 
of filings congregating about the poles of a 
magnet. This fact has given considerable prob- 
ability to the suggestion that the solar corona 
is due to some electro-magnetic discharge from 
the sun’s surface. 


CORRECTED LENS 


A lens having the chemical and visual foci 
coincident. A properly achromatised lens is 
said to be under-corrected when, in spite of the 
addition of a second glass, the blue rays still 
come to a focus nearer the lens than the yellow, 
and over-corrected when the blue rays come to 
a focus behind the yellow ones. 


CORRECTION COLLAR 

A rotating collar sometimes fitted to high-class 
microscopic objectives. The varying thicknesses 
of the cover glasses placed over microscopic 
objects affect the value of the corrections of 
high-power objectives. The correction collar 
overcomes this difficulty by varying the separa- 
tion of the combinations of the objective. 


CORROSIVE SUBLIMATE (See ‘“ Mercuric 
Chloride.’’) 


COSMICAL PHOTOGRAPHY 

So many different subjects requiring special 
treatment are included in the general class of 
celestial or cosmical objects that for the majority 
of them it will be more satisfactory to describe 
the methods of photographing them under their 
respective special headings (which see below). 
As regards the actual photographic details of 
procedure, however, mutch that is common to 
all celestial photography may most conveniently 
be detailed here. 

Apparatus.—This will vary from the hand 
camera to the powerful and specially adapted 
mechanical camera of the astronomer; they will 
all, however, have in common the feature of 
being focused for parallel rays, or, as it is 
usually termed, set for infinity. The reason 
for this is that for all practical purposes all celes- 
tial objects are so far distant from the earth 
that any differences between their respective 
distances are inappreciable. This fact will to 
many constitute a considerable simplification, 
as undoubtedly the use of a “fixed focus’’ 
camera admits of apparatus being efficiently 
used in a condition which would be much too 
rough for photographing objects whose distances 
were different. In photographic language there 
is no “depth of focus” difficulty in celestial 
photography, and the flatter the field of defini- 
tion given by the lens the more satisfactory will 
its performance be. This leads at once to the 
fact that for photographing large areas of sky 
the modern anastigmat type of lens, giving 


Cosmorama 


critical definition over a large angle, is the 
most efficient instrument. 

In many cases the question of cost may serve 
to prohibit the employment of a sufficiently 
large lens camera—or refractor, as it is usually 
termed—and work of the highest type of accuracy 
has been done with concave mirror cameras. 
These involve only the optical working of one sur- 
face, and thus for a given sum the instrument 
may be of a much greater power. Two kinds of 
reflector have been principally used: speculum 
metal and silvered glass. The former were excel- 
lent, but when they tarnished it was exceedingly 
difficult to re-polish them without altering the 
shape of the reflecting surface and thus destroy- 
ing the definition of the image. Most of the 
reflecting telescope cameras now in use consist 
of a surface of glass accurately ground to a 
parabolic form and then coated over with an 
exceedingly thin film of pure silver. This offers 
the important advantage that when it becomes 
tarnished it can be dissolved away in a few 
minutes and replaced very quickly with a new 
film without in any way interfering with the 
shape of the glass surface. 

Plates.—For most kinds of celestial photo- 
graphy, excepting that of the sun and moon, 
it is advisable to employ the fastest plate obtain- 
able, provided that the grain is not noticeably 
prominent. On account of the subjects being 
generally of special coloration, the isochromatic 
or panchromatic plates now so easily obtainable 
should be preferred to the non-colour sensitive 
brands, as without them it may be found im- 
possible to render differences which are quite 
easily noticeable to the eye. 

Development. — This will, in general, be 
exactly the same process as would be used for 
ordinary terrestrial photography. Again except- 
ing photographs of the sun and moon, the 
general tendency will be for under-exposure to 
be experienced, so that the treatment recom- 
mended for this should be the normal procedure 
for astronomical work if harshness in the results 
is to be avoided. Any of the standard developers 
may be employed with practically equally good 
result. Pyro soda, metolquinol, and rodinal 
are all used by some of the best workers, and 
there is little to choose between them. In general, 
no bromide or other restrainer should be used ; 
the negative should be thin and full of detail 
rather than dense and contrasty. To further this, 
development should never be over-done, as it is 
practically impossible to remedy it by subse- 
quent reduction, whereas a thin negative, with 
detail, may be gradually intensified and re- 
intensified, by means of mercuric chloride and 
ferrous oxalate, until the requisite density is 
obtained. 

For copies all the usual media are available. 
Lantern slides of good astronomical subjects 
make beautiful and interesting records. 


(For details of various subjects see ‘‘ Comets, 


Photographing,” ** Corona Photography,” 
*‘ Eclipses,” ‘“‘ Lightning,’ ‘‘Moon,” ‘Nebula,’ 
*‘ Rainbow,” “‘Stars,’”’ “Sun,” etc.) C. P. B. 


COSMORAMA (Fr., Cosmorama; Ger., Kos- 
morama) 


An early arrangement for the inspection of 
photographs or pictures. These were laid 


150 


Covering Power 


horizontally on a semicircular table or platform, 
each picture having an inclined mirror to reflect 
it to a viewing lens, at which the spectator’s 
eye was placed. The pictures were illuminated 
by concealed lamps and were inspected in 
turn. 


COSMORAMA STEREOSCOPE (Fr., Stéréo- 
scope cosmorama; Ger., Kosmorama 
Stereoskop) 

An early form of stereoscope made by Messrs, 
Knight, in which two large lenses were used 
having a segment cut off, so that they could be 
placed with their centres 3 in. apart. 


COTTON-WOOL 


Prepared from the hairs of the seed of gos- 
sypium Barbadense and other species of gos- 
sypium. It has many uses in photography, and 
the variety known as absorbent cotton and sold 
in rolls, wrapped in blue paper usually, is the 
best to use. The very common and coarse 
variety used for packing should not be used for 
wiping wet negatives, as it contains grit and 
other coarse foreign matter, which is apt to 
scratch gelatine. All negatives should be wiped 
eatin! the final washing with a wet pad of cotton- 
wool, 

This material also makes a serviceable filter 
for liquids, a tuft being lightly placed in the 
neck of a funnel and the liquid filtered through 
it. It does not filter as thoroughly as filter 
papers, but it will serve for some liquids, par- 
ticularly varnishes. 

In process work, cotton-wool has numerous 
uses, and the “ absorbent’? wool is commonly 
preferred. A wad of it is generally found the 
handiest means for cleaning zinc or copper with 
pumice powder or whiting to remove grease. 
The absorbent cotton is also used for filtering the 
albumen-bichromate or fish-glue solutions. The 
development of albumen-bichromate inked prints 
is effected with the help of a tuft of cotton. By 
its means, too, the scum which sometimes forms 
on wet-plate negatives can often be effectually 
removed without damaging the negative. 


COVER GLASS 

A plain glass bound up with a transparency 
(lantern slide) to protect the film. Also a plain 
glass used as a cover for the object on a micro- 
scopic slide. 


COVERING POWER (Fr., Pouvoiy 2 cowvrir ; 
Ger., Deckkraft) 

The extent, or boundary, to which a lens will 
produce a well-defined and properly illuminated 
image. The circle of illumination produced by 
a lens is practically the measure of its covering 
power; but definition must also be considered, 
for this may not be equally good all over the 
circle. It is desirable to have a lens which will 
cover a slightly larger circle than is sufficient 
to include the size of plate used; otherwise 
there will be a falling-off of definition and of 
light when using the rising front. The better 
the lens the more satisfactory should be its 
covering power; a good modern anastigmat 
will readily cover, when stopped down, a plate 
at least a size larger than that for which it is 
intended. 


Cowan’s Developer 151 


COWAN’S DEVELOPER 
A formula advocated many years ago by 
A. Cowan for use with negatives. 


No. 1.—Pyrogallic acid 20 grs. 4 g. 
Nitric acid 2 drops *§ ccs. 
Water to. 100%: 1,000 ,, 

No. 2.—Strong liquor 

ammonicz ef OZ. 25 ccs. 
Potassium  bro- 

mide... - 374 gers. 8 g. 
Water to. iO Os, 1,000 ccs. 


In cases of ordinary exposure mix in equal parts. 
For under-exposure add more of No. 2, and for 
over-exposure more of No. 1 and bromide. 

A. Cowan also prepared a solution of pyro- 
gallic acid which is always ready for use. 


Pyrogallic acid . Ht OR. 18.3: g. 
Citric acid . : -« 6O gts. 2°25 ,, 
Water to ‘ - 544 OZ. 1,000 ccs, 


Dissolve the citric acid in water and add the 
pytogallic. The solution will contain 8 grains 
of pyro to the ounce of water, and will keep good 
for many months. In using it dilute according 
to formula employed. 

Another developer known as ‘“‘ Cowan’s”’ is 
the following (known also as a citrate of iron 
developer), recommended for chloride lantern 
plates :— 


No. 1. For cold tones— 
Potassium citrate . 100 gts. 200 g. 
Potassium oxalate Sen toner GO ,, 
Hot distilled water to . 1 0z. 1,000 ccs, 
No. 2. For warm tones— 
Citric acid ; 90 grs. 180 g. 
Ammonium carbonate 60 ,, 120 ,, 
Cold distilled waterto . 1 0z. 1,000 ccs. 
No. 3. For extra warm tones— 
Citric acid . 130 grs. 260 g. 
Ammonium carbonate 40 ,, 80 5, 
Cold distilled water to . I 0z. 1,000 ccs. 


In mixing solutions Nos. 2 and 3 it is better 
to put the crystals into a deep vessel, and, after 
adding the water, leave alone until all efferves- 
cence ceases, It is advisable to make it over- 
night. To 3 parts of any of the above solutions 
add 1 part of the following at the time of using :— 


240 g. 
2’ ‘ccs. 
Tyooo fs, 


Ferric sulphate . 
Sulphuric acid . : 
Distilled water to . 


COXIN 

A solution of crocein scarlet 3 B and a yellow 
dye, in which exposed plates were bathed, or 
which was added to the developer so that they 
could be developed in daylight; the subject of 
a German patent in 1902. 


C.P. 

The initial letters of the words “ Candle- 
power” (which see). Also an American term 
placed after the name of a chemical to indicate 
that it is chemically pure. 


CRACKED NEGATIVES . 
Negatives are easily cracked if cheap frames 
with uneven beds and imperfect springs are 


» 120 gts. 
I drop 
I OZ. 


Cracked Negatives 


used, The crack may at first appear slight and 
unimportant, but in time it invariably extends 
across the plate. With care the film on a cracked 
negative need not be broken; merely bind the 
negative to a piece of glass of the same size by 
means of gummed strips of paper, or cement it 
bodily to the glass by means of a mixture of 
Canada balsam and benzole or xylol, the crack 
being first of all filled in with the mixture. 
Many workers duplicate cracked negatives in 
the following manner. First paint on the glass 
side and along the crack a fine line of Brunswick 
black or other opaque varnish, and then make 
a positive transparency, on which, of course, the 
crack will be represented by a thin white line. 
Then, by means of a retouching pencil or a 
camel-hair pencil and suitable medium, retouch 
the white line, and make a negative from the 
transparency. Much depends upon the position 
of the line and the degree of skill exercised. 
There are two systems of taking a print from 
a cracked negative without the crack showing, 


A. Printing from 
Cracked Negative 
on Revolving Frame 


B. Cracked Negative 
at Bottom of Deep 
Box 


but the work must be done in daylight. One 
is to place the frame on a board attached to 
strings A, and to keep the board swinging or 
rotating in the shade while the picture is being 
printed. Another is to place the frame at the 
bottom of a deep box B, also in the shade. These 
methods are rather slow, but they give the best 
results possible with cracked negatives, 

It is, of course, possible to remove an unbroken 
gelatine film from a cracked glass, and one of 
the best methods of doing so is the following : 
Carefully clean a sheet of glass one size larger 
than the negative to be treated, place the cracked 
negative, film side upwards, upon it, and coat 
evenly with enamel collodion. 

Put on as much as the film will hold without its 
running over, allow to set thoroughly, and wash | 
till the water runs freely off it; drain, and coat 
with a solution of 20 grs. of gelatine in I oz. 
of warm water, and allow to set thoroughly. 
Then immerse the cracked negative with its 
prepared film in this mixture :— 


Hydrofluoric acid 60 drops 6 ccs. 
Glycerine ‘ Paar tid sy a, 
Alcohol ° . wre . Ee 
Water to ° Te ies, 2.000: 5, 


Cracks in Varnish 


In a few minutes the film will be free at the edges, 
and it should then be carefully coaxed off the 
glass by means of a camel-hair brush and trans- 
ferred to a dish of cold water. Slip under the 
released film a sheet of glass coated with gela- 
tine solution made as already stated; or use 
an unexposed dry plate that has been fixed and 
washed. Coax out any wrinkles with the camel- 
hair brush or by blowing, and allow to dry in a 
horizontal position. If the cracked negative has 
been varnished, all traces of the varnish must be 
removed before any attempt is made to remove 
the film. (See ‘‘ Varnish, Removal of.’’) 

It is possible to do without the collodion, and 
so simplify the work of transferring the film, 
but greater care will be necessary. Immerse the 
negative in 12 oz. of water to which 60 drops of 
hydrofluoric acid have been added, and after 
the film becomes loose at the edges, coax it off 
very gently in the manner already described. 
Wash for about ten minutes, at the end of which 
time the film will be enlarged considerably; if 
required it can be left in the enlarged state, but 
otherwise it must be immersed in a solution of 
equal parts of water and methylated spirit until 
it has contracted to its original size. Then 
float it upon a gelatine plate as above described. 

In the case of a cracked new negative the 
film may be removed by soaking for about thirty- 
six hours in a cold saturated solution of common 
washing soda; all the after operations are as 
described in the preceding paragraph. 

Cracked negatives other than gelatine are best 
treated as broken negatives (whtch see). 


CRACKS IN VARNISH 

Cracks upon varnished collodion plates are 
more common than upon gelatine plates. Nega- 
tive varnish is essentially a gum or resin dis- 
solved in a volatile solvent. When the varnish is 
spread over the surface of the film, the solvent 
evaporates and leaves a coating of the gum 
resin on the film; as the resin dries it contracts 
and sometimes cracks. Circumstances that lead 
to cracking are (1) making the varnished negative 
too hot (either by heating for the purpose of 
hurrying the evaporation or by printing in a 
hot sun); (2) insufficiently washing after fixing ; 
(3) storing ina damp place; and (4) using an 
unsuitable varnish. 

Cracked varnish on a collodion negative may 
be remedied to an extent by rubbing finely- 
pent lampblack, or soot, into the cracks 

y means of the dry finger-tip or a piece of 
chamois leather, and then revarnishing. 

Cracked varnish on modern gelatine negatives 
may be treated in the same way, but it is better 
to remove the varnish entirely and then revar- 
nish. To remove varnish, soak i the solvent 
which was used for the varnish; if this is not 
known, methylated spirit may be tried, as most 
of the resins, etc., used for varnishes are soluble 
in spirit. After a good soaking rub with cotton- 
wool and give the negative one or two more 
soakings in spirit, so as to get rid of the last 
traces of the varnish. A little ammonia may be 
added to the second spirit bath with good effect. 


CRAPE MARKINGS 


A defect met with in wet collodion work, and 
taking the form of markings having the appear- 


152 


Cristoid Film 


ance of crape or fine net work. They are due 
to the use of too gelatinous collodion or a strong 
cadmium bromo-iodiser. Solvents too much 
diluted with water may also cause the defect. 


CRAWLING 


A developer is said to “ crawl’ when it does 
not flow evenly over the film, being prevented 
from doing so by the greasy surface caused by 
the faulty condition of the collodion bath; 
crawling may also be due to an excess of alcohol 
in the developer. Printing paper is said to 
“crawl”? when it expands or contracts during 
the progress of printing, as some papers are 
prone to do. If, for example, a bone-dry paper 
is put into a frame and placed out of doors in 
damp weather, the paper may expand during 
ptinting and cause blurred outlines of the image 
to appear. Damp paper put out to print under 
a negative on a hot day will sometimes show 
the same effect, through contracting while 
printing. The defect is more common with 
albumen paper than any other. 


CRAYON ENLARGEMENT (Fr., Agrandisse- 
ment au crayon; Get., Stift-Vergroésserung) 
An enlargement usually on rough-surfaced 
bromide paper, worked up with crayons. ‘The 
proportion of hand-work may vary greatly, 
from the mere removal of spots and blemishes 
to an elaborate amount. Much of the black- 
and-white work now seen on bromide enlarge- 
ments is, however, done with the aerograph. 


CRAYONS (Fr., Crayons; Ger., Stifte) 

Small pencils of pipeclay, kaolin, or chalk, 
incorporated with various mineral or metallic 
pigments, and used for drawing, working-up 
enlargements, prints, etc. They are obtainable 
in the form of chalks, as loose points for adjust- 
able holders, or enclosed in cedar pencils. Those 
employed on enlargements are known as bromide 
pencils (which see). Coloured crayons are used 
for introducing backgrounds into carbon prints. 

In process work, lithographic crayons, consist- 
ing of a mixture of wax, shellac, soap, and lamp- 
black, are largely used. A wet-plate half-tone 
negative can be locally intensified by rubbing a 
crayon gently over the part where strength is 
desired. Half-tones can be stopped out for 
fine etching and vignetting by the use of the 
crayon wherever required. Lithographic crayons 
are preferred to black chalks for drawing on 
gtained papers and scraper boards for reproduc- 
tion, because the work is fixed, owing to its 
waxy or greasy nature, without further treat- 
ment. 


CREAM OF TARTAR 
A common name for acid potassium tartrate, 
(See ‘‘ Potassium Bitartrate.”’) 


CRESCO-FYLMA 

A name given to a film-stripping and enlarging 
solution introduced in 1891, the patent on which 
has now, of course, expired. (For similar 
solutions, see “ Film Stripping.’’) 


CRISTOID FILM 
A gelatine film introduced as a substitute for 
glass plates or celluloid, and consisting of two 


Critical Angle 


coatings, the lower one being a slow emulsion 
and the upper one a fast emulsion, The chief 
advantage claimed was that errors in exposure 
were eliminated, because if the upper film was 
over-exposed a good negative would be obtained 
on the lower film; also halation was entirely 
obviated. The film before development was 
treated with formaline, and, after the usual 
operations, squeegeed down to plate glass, a 
bath of alcohol and formaline being used to cause 
the film to contract to its original size. If this 
bath was omitted, the expansion of the gelatine 
due to the absorption of water during the opera- 
tions of developing, fixing, and washing gave 
enlarged negatives. 


CRITICAL” ANGLE 

The angle at which a ray passing through a 
transparent substance is totally reflected. If a 
thick plate of glass be held between the eye and 
a light the critical angle will be reached when the 
inner surface of the glass, either upper or lower, 
according to position, reflects as from a silvered 
surface. 


CRITICAL ILLUMINATION 

In microscopy, critical illumination is obtained 
by arranging the illuminant, mirror, and substage 
condenser in such a manner that the image of 
the lamp flame is seen in the centre of the field 
when looking through the microscope. Critical 
illumination is not practicable with low powers, 
but it is essential when obtaining the finest 
definition a lens which will give with high powers, 
and more especially when using the immersion 
lenses. Recent experiments have shown that 
critical illumination has been obtained when the 
back lens, on looking down the tube without an 
eyepiece, is just filled with light. Daylight can- 
not be used for critical work. The Nernst lamp 
is a convenient light for photo-micrography, but 
for visual purposes an oil-lamp with 4-in. wick 
gives excellent results. The lamp, with the 
flame edgeways to the microscope, should be 
placed with the wick about 9 in. in front of the 
mirror, which must have the plane side turned 
to the light. The mirror is placed so that the 
light is reflected in a direct line through the 
substage condenser and objective. A diatom 
slide is placed on the stage and the substage 
condenser racked up and down till the image 
of the flame is seen in the centre of the field. 
If the eyepiece is now removed, the back lens 
should (providing the substage condenser is of 
sufficiently high aperture) be filled, or nearly 
filled, with light. That portion of the field of 
view only which contains the image of the lamp 
flame gives critical definition. 

If the flame image is a disturbing factor to 
the work in hand, it can be removed by slightly 
lowering the condenser, but the definition suffers. 
Critical illumination is necessary only for powers 
of + in. and upwards. Low powers should be 
worked without the substage condenser, and 
with the concave surface of the mirror turned 
to the light. 


CROOKES’ TUBE 

The high-vacuum tube (named after the in- 
ventor) which produces the X-rays. In an 
X-ray tube the vacuum is brought to less than 


( 


153 


om 


Crystal Varnish 


one-millionth of the density of the atmosphere. 
In the original Crookes’ tube the cathodal rays 
were allowed to fall on the glass; this was 
improved by Prof. Jackson, who caused the 
cathodal rays to fall on a metal plate connected 
with the anode (anti-cathode). Another improve- 
ment was the cupping of the cathode to allow 
all the cathode rays to fall on one spot on the 
anti-cathode, this arrangement constituting the 
“focus tube.” (See also under the heading 
“X-ray Photography.”’) 


CROSS FRONT (Fr., Décentrement horizontal ; 
Ger., Kreuz-Objektivbrett) 

A provision for moving the lens of the camera 
sideways, so that a little more of the subject 
may be included at one side or the other, without 
having to shift the apparatus. It generally 
consists of a panel sliding in grooved rails, with 
a clamping screw to maintain its position when 
adjusted. 


CROSSED LENS 
A crossed lens is one having its two sides of 
a similar nature, either concave or convex, but 


B. Convex 
Crossed Lens 


A. Concave 
Crossed Lens 


of different curvatures, as illustrated at A and B. 
CROWN GLASS (See “ Glass.’’) 


CRYSTAL CUBE (Fr., Cube de cristal; Ger., 
Krystall Kubus) 

A stereoscopic device, invented by Henry 
Swan, depending on an application of the angle 
of total reflection of glass surfaces. Two 
rectangular glass prisms are ground to an angle 
of 39° or 40°, and are placed with their widest 
sides in contact, or nearly so. One of a pair of 
stereoscopic photographs is attached to one side 
of the prism combination, and the other behind. 
On inspection, the rays from the picture at the 
back of the glass are transmitted direct to one 
eye, while those from the second picture are 
reflected from the surface of the prisms where 
they touch to the other eye, and appear as if 
also coming from the back. The two pictures 
therefore coalesce, giving stereoscopic relief, 
the effect being as if a solid object were imbedded 
in the glass, 


CRYSTAL MARKINGS (Fr., Marques 
cristallines ; Ger., Krystall Bezeichnen) 
Crystalline or tree-like markings on or under 
the film of a collodion or gelatine negative. 
They are usually due to insufficient washing 
after fixing, and sometimes they do not appear 
till many days have elapsed. 


CRYSTAL VARNISH 
A particularly clear varnish, used mostly for 
lantern slides, autochromes, and other trans- 


Crystallisation 154 


parencies. There are many different formule, 
and for lantern slides the following is one of 
the many suitable :— 


Gum dammar » S28 gts, 52 g. 
Benzole. : O78 602.0 Se Ooonecs. 


Apply this cold. For autochromes a stronger 
solution should be used, namely, 1 oz. of dammar 
in 5 oz. of benzole, and the plate should be 
warmed slightly before the varnish is poured on 
(but see ‘ Autochrome Process,” where a further 
formula will be found). 

Equal parts of pale Canada balsam and rectified 
oil of turpentine make a good crystal varnish 
for maps and engravings, but for fixing pencil 
drawings 1 oz. of mastic dissolved in 6} oz. of 
rectified spirit is recommended. It is not 
advisable to use crystal varnish for negatives, 
shellac varnish being better, Another crystal 
vatnish is that known as celluloid varnish, 
which is largely used for lantern slides. It is a 
solution of celluloid in acetone or other solvent. 


CRYSTALLISATION (Fr., Cristallisation ; 
Ger., Krystallisation) 

A substance or salt when dissolved in water 
to saturation will gradually deposit crystals, 
or crystallise out if the water be evaporated. 
This is called ‘‘ wet crystallisation.” Some- 
times a dry salt is fused and allowed to cool, 
when crystals will also form; this is called 
“crystallisation by fusion.” Again, a volatile 
salt may be heated, when it will go off in the form 
of vapour and crystallise on a cool surface; 
this is “‘ crystallisation by sublimation.” 


CRYSTALOTYPE 

An old name for photographic transparencies 
upon glass, either in the form of lantern slides 
or larger plates for window decoration. It was 
the original English name, “ hyalotype”’ being 
the American. 


CRYSTOLEUMS 


Photographs coloured to give the appearance 
of direct paintings upon glass; known also as 
chromo-photographs. The system of colouring 
is about two centuries old, and, before the days 
of photography, engravings and prints were 
used as a base, the process being known generally 
as mezzotinto painting. The advent of photo- 
gtaphic prints on paper did much to revive the 
interest in colouring processes. A modern 
crystoleum print properly finished looks, as is 
intended, like a painting upon glass, but actually 
a transparent photograph comes between the 
colouring and the glass. The diagram shows 
the construction of a crystoleum photograph. aA 
is the front glass, on which a photograph B is 


pasted face downwards. When dry the photo- | 


gtaph is made transparent, and delicate details 
coloured with ordinary oil colours, but the 
broad masses of colour are not put on. Another 
glass D, of the same size and shape as A, is put 
at the back, but is prevented from touching the 
photograph by means of strips of paper H, 
which leave a small space at c. On the back & 
of the second glass are painted the broad masses 
of colour. The whole is backed up with a piece 
of flat cardboard or other backing G, leaving a 
Space F. When viewed from the front the colours 


Crystoleums 


are seen through the transparent photograph, 
and the whole has the appearance of a delicately 
painted picture upon glass. 

The working details are as follow: A suitable 
ptint is made upon albumen paper, which is the 
only photographic paper suitable, it being thin 
and tough. The print is placed in hot water 
until it becomes quite flaccid, and is then made 
surface dry by pressure between clean white 
blotting-paper. A piece of convexo-concave 
glass (flat glasses are not so suitable), sold 
specially for the purpose, is then made quite 
clean, and its concave side coated with clear 
starch paste or warm gelatine. The damp 
print is laid paper side downwards upon a flat 
piece of glass, and its face is coated with the 
adhesive selected. The printis then placed face 
downwards in contact with the inner (concave) 
and prepared surface of the glass, and pressed 
into close contact. The surplus paste must be 
removed from between the print and the glass, 
this being accomplished best by laying a piece 
of wet parchment over the back of the damp 

print, pressing out the ad- 

Ek a hesive with a knife handle 

or toothbrush handle. The 
paste must be expelled, also 
all air-bubbles, by a not too 
firm pressure, which must be 
worked always from the centre 
of the print to the extreme 
margin. When in perfect con- 
tact the parchment is taken 
away, the back of the print 
wiped free from any super- 
fluous adhesive, and the whole 
put aside to dry thoroughly. 
The correct mounting of the 
picture is most important, as 
any errors will spoil the effect. 

When dry the print must be 
made transparent, and this is 
accomplished in one of two 
ways—namely: (1) Rub the 
back of the print with glass- 
paper in order to remove as much of the 
paper as possible (the actual picture being, of 
course, underneath, next to the glass); a medium 
glasspaper is used at first, followed with a very 
fine one in order to remove all scratches, and to 
lessen the possibility of suddenly penetrating 
the actual picture on the albumen. When the 
bulk of the paper has been evenly rubbed away, 
the glass side of the picture is warmed before 
a fire, or over a gas-stove, and at the same time 
a piece of paraffin wax is rubbed on the paper 


Ss SQ 
SHI 
SHS 


AAV RAY 


SRNANHF MAN 
Pa 
Pe-whe? 


SS ss 


“ES eee, 
: 


SSSA 


NAAR 


SS 


Oo 7 mm OO WD PD 


SSN 


SWS 
S 


Section of 
Crystoleum 


side of the print, the object being to saturate 


the picture with warm wax. When the print 
appears equally transparent all over, all super- 
fluous wax is removed with a piece of flannel 
and the picture allowed to cool. When cold 
the wax may be further polished, and if not 
evenly transparent it must again ke glass- 
papered on the dense parts and waxed again. 
(2) The alternative process consists in leaving 
the paper print of its original thickness and 
making it transparent by rubbing into it a 
solution of 4 oz. of Canada balsam in 3 oz. of 
either benzene or chloroform, the former being 
the cheaper. Another solution for the purpose 
is Canada balsam 2} oz., paraffin wax 1 0Z., 


on 
a — xt 
a a ee 


oa 


Cupric 


and white wax 1 oz., heated together and used 
in the same way as the wax in the first 
method. 

Upon the print prepared as described all 
the fine details are now coloured, these includ- 
ing the lips, eyes, jewellery, etc. A finely- 
pointed sable brush is used, and ordinary oil 
colours slightly diluted with megilp. After the 
colouring, the second glass is put on at the back 
and bound by the edges to the first one to keep 
it in position. It must be as close as possible 
to the first glass, but not touching, and it may 
be kept from contact by sticking two or three 
thicknesses of stamp edging along the edges 
of the front of the second glass; or a narrow 
strip of thin cardboard may be used in the same 
way. The colouring on the second glass may be 
very crude, the masses of colour being put on 
the back and care being taken not to overlap 
the outlines. No details or lights and shades 
are wanted, as they appear in the picture itself, 
but body colours only are wanted, these being 
mixed with a proportion of flake white. The 
colour already in the print must be considered ; 
consequently, to picture fair hair in a portrait, 
white tinted with yellow will serve. Upon view- 
ing the picture from the front (holding it over 
white paper), one can easily judge whether the 
colouring is correct or not. If not, it may be 
corrected or removed with a rag and turpentine. 

The final operation consists in attaching a piece 
of white cardboard to the back of the second 
glass and binding the whole together by means 
of narrow paper strips, and then framing. Fancy 
gilt frames are the most suitable, but obviously 
any may be used. Special solutions for mount- 
ing the pictures, making them transparent, and 
for preserving the transparency and colouring, 
are articles of commerce. Fs, 


CUPRIC 
An adjective derived from cuprum, the Latin 
word for copper. (See “* Copper.’’) 


CUPROTYPE 

A printing process invented in 1857 by 
C. J. Burnett, of Edinburgh. It was on the lines 
of the ink process (which see), copper chromate 
(cupric chromate) being used. 


CURVATURE OF FIELD (Fr., Courbure du 
champ ; Ger., Bildwilbung) 

Synonym, aberration of form. A defect in a 

lens whereby the image of a flat object does not 


Curvature of Field 


lie on a plane surface, but on a curved or saucer- 
Shaped one. Thus, as shown in the diagram, 
the rays forming the image of the arrow UV 


155 


Curvilinear Distortion 


render it in space at y xX as curved instead of 
straight, the result being that if the centre of 
the image is focused the margins will be out of 
focus, and vice versa. Curvature of field must 
not, however, be confused with curvilinear dis- 
tortion (which see)—a not uncommon mistake— 
for the arrow will be shown as straight on the 
focusing screen, although of unequal definition 
along its length. When a lens is subject to 
curvature of field the best result is obtained by 
focusing for a point midway between the centre 
and the margins of the picture, as shown by 
the dotted line, and using a small stop. Curva- 
ture of field may be reduced in compound lenses 
by increasing the separation, but only at the 
expense of astigmatism. The introduction of 
the new Jena glasses has rendered it possible 
to obtain lenses at once free from astigmatism 
and possessing a flat field. 


CURVILINEAR DISTORTION (Fr., Distor- 
ston; Ger., Verzeichnung, Distorsion) 

An aberration occurring in a single lens, 
whether consisting of only one glass or of several 
cemented together, which causes straight lines 
at the margins of the picture to appear curved. 
If the diaphragm c is in front of the lens, asin A, 
the image of the square D shows “ barrel-shaped ”’ 
distortion ; while when it is behind the lens, 
“pincushion ”’ distortion is present, as in B. 
The barrel distortion is usually considered less 
objectionable, and all single lenses are now fitted 
with the diaphragm in front. Distortion de- 
creases as the focal length of the lens becomes 


B. Pincushion Distortion 


greater, being most apparent in short-focus 
objectives. It is obviously objectionable for 
architectural work, or anything requiring accur- 
ate reproduction of straight lines. The position 
of the stop has an important influence ; if it is 
brought nearer to the lens distortion is reduced, 
but, unfortunately, at the expense of definition. 
Curvilinear distortion is completely cured in 
doublet or “rectilinear” lenses by placing the 
stop in the centre between the two combinations, 
when one kind of distortion neutralises the 
other. It is owing to this fact that distortion 
in a negative may be corrected in enlarging, if 
the same lens is used as the negative was taken 
with ; for in the enlarging lantern the previous 
position of the stop is reversed, coming between 
lens and image (enlargement), instead of between 
lens and object, which in this case is the 
negative. 


Cutch 


CUTCH (See “ Catechu.’’) 


CUT-OUT MOUNT 

A sheet of cardboard in which an opening— 
rectangular, circular, oval, etc.—has been cut, 
generally with a bevelled edge. The print is 
mounted on a second board, which is placed 
behind the other. This method of mounting is 
more generally employed for drawings and 
sketches than for photographs. 


CUTTING 

A term used in connection with the sharpen- 
ing up of the dots in making half-tone negatives, 
as referred to under many separate headings. 
(See, for example, “‘ Clearing Solutions.’’) 


CUTTING SHAPE, OR MOULD 
Calibre; Ger., Beschnetdeglaser) 

A template used to guide the cutting knife 
in trimming prints. It is commonly made of 
plate glass, though zinc and other metals are 
occasionally employed. Cutting shapes are 
obtainable in all sizes, and may be square, oblong, 
circular, oval, etc. Curiously enough, it is 
difficult to get a rectangular glass cutting shape 
with absolutely true and parallel sides. This, 
combined with the unfortunate ease with which 
the shapes slip, even in practised hands, together 
with their liability to get broken or chipped, no 
doubt explains the growing popularity of guillo- 
tine cutters and print trimmers. Cutting shapes 
with the lower side ground are less slippery 
than those of plain glass. 


CYANIDES 

Salts formed by the combination of a metal 
with the radicle CN. An example is potassium 
cyanide, KCN. 


CYANINE (Fr., Cyanine ; Ger., Cyanin) 

Synonyms, cyanine iodide, quinoline or chino- 
line blue, diamylcyanine. C,,H,,N,I. Molecular 
weight, 544. An aniline dye obtained by the 
action of caustic potash on an alcoholic solution 
of lepidine-iodo-amylate and _ chinoline-iodo- 
amylate. Itwas for some years the only practical 
red sensitiser known, but its action was extremely 
uncertain and its sensitising power weak, and it 
has been entirely superseded by the newer iso- 
cyanines. It occurs in monoclinic crystals having 
a green metallic lustre, and gives a rich blue 
solution in water and a more reddish one in 
alcohol. The aqueous solution is extremely 
sensitive to light. Cyanine bromide, chloride, 
sulphate, and nitrate can be prepared by treat- 
ing the iodide with the respective silver salts 
but they act in the same way as the iodide. 


CYANOFER AND CYANOGRAPHIC 
PROCESS 
Names sometimes given to the Pellet process 
(which see). 


CYANOGRAPH 

A photographic device for recording the blue 
light in the atmosphere; invented in 1903 by 
Maillard and Reiss, of Belgium. ‘The apparatus 
consists of a driving clock which, at regular 
intervals, unrolls a short length of a band of 
sensitive paper, on which is made an exposure, 


(Fr., 


156 


Cycle, Camera on 


a suitable blue filter being interposed. It has 
been used chiefly for attaching to captive 
balloons for the purpose of testing light in high 
altitudes. In X-ray photography a piece of » 
card is used as a filter, and the rest of the 
apparatus enclosed in a lead casing. 


CYANOTYPE PROCESS, NEGATIVE (See 
** Blue-print Process.’’) 


CYANOTYPE PROCESS, POSITIVE (See 
** Pellet Process.’’) 


CYCLOGRAPH _(Fr., 
Cyklograph) 

A panoramic camera designed by A. H. 
Smith, by which the whole outer circumference, 
or any portion, of a cylindrical object—such as 
a vase—may be photographed on a single flat 
plate. The object is supported on a circular 
platform, which is made to roll along a straight 
guiding surface at a right angle to the axis of 
the lens, so that as it moves forward it also 
revolves, like a carriage wheel advancing. This 
is, in fact, making use of the principle of a 
cycloidal rotation. At the same time, an 
Opaque screen having a natrow vertical slit is 
made to travel on a parallel path at a speed 
proportionate to that of the object, in such a 
manner that each successive portion of the 
object is exposed to the lens when nearest to 
the straight surface—or, in other words, when 
it is at the cusp of a cycloid, and its movement 
is consequently infinitesimal. 

The name cyclograph is also given to a 
panoramic camerainvented by Mons. Damoizeau, 
which turns in a complete circle, so that the 
entire horizon, or the inside of a circular build- 
ing, may be photographed. A band of film is 
employed, and several circles may be taken in 
succession on the same band if required. 


CYCLE, CAMERA ON 

There are many opinions as to which is the 
best plan of carrying a camera on a cycle, much 
depending upon the size of camera and amount 
of apparatus it is desired to carry. Many of 
the pocket and folding cameras need not be 
considered, as they go into the pocket and do 
not inconvenience the rider in any way; but 
it is advisable to carry them in an inner pocket 
rather than an outside one, chiefly to protect 
them from road dust. A favourite method of 
carrying larger and unpocketable cameras is to 
strap them firmly to the middle of the back of 
the rider; very broad shoulder-straps will be 
found less tiring than narrow ones. If the 
camera is not held firmly it may work round 
under the arm, and cause considerable incon- 
venience when riding, and possibly an accident 
when dismounting or turning a corner. Com- 
mercial carriers are made to fix either in front 
of the handle bars or behind the saddle. Front 
carriers are to be preferred, as the camera is 
then always in sight ; if placed behind the rider, 
it is apt to be forgotten when dismounting, and 
the rider may be thrown. Cameras when carried 
on a cycle should always be wrapped in a water- 
proof focusing cloth or other covering, or be 
enclosed in a proper bag or case, in order to 
protect them from road dust, which otherwise 


Cyclographe; Ger., 


Cyclol 


will cause pinholes on the negative, and possibly 
interfere with the working of the shutter and 
plate- changing mechanism. Tripods may be 
strapped to the handle-bar, on the fork of the 
machine, etc. ; some individuals prefer to strap 
them under the flap of the case, which rests 
on the front carrier, and attach the projecting 
ends to the handle-bars. 


CYCLOL 

A one-solution developing mixture introduced 
in 1892, and consisting of rodinal, eikonogen, and 
hydroquinone. (See “Developers, Mixed.’’) 


CYLINDERS, GAS 

Annealed steel cylinders, tested hydraulically 
to withstand a pressure of 3,000 lb. per square 
inch, and charged with compressed gas—oxygen, 
hydrogen (generally, coal-gas), dissolved acety- 
lene, etc. Periodical re-annealing is necessary, 
and the gas compressing companies will not take 
the risk of filling cylinders unless their regula- 
tions in this connection are complied with. The 
construction of the valve is such that all dust 
and grit should be prevented from entering it ; 
and therefore before connecting the fittings the 
valve should be opened for an instant so that 
the rush of gas may dislodge anything in the 
way. Cylinders of compressed gas are used by 
the lanternist, who must become familiar with 


Section of Cylinder Valve and of the Stem 
and Adapter of Fitting 
the working of the valve, a cross section of which 
is shown in the illustration. The valve is 
screwed into the cylinder, the gas from which 
leaves by the narrow passage A when the spindle 
B is slightly withdrawn by turning its squared 
portion c by means of a key; the gas passes 
to the lantern fittings through the inverted 
cone D. The gas-tight joint with the automatic 
regulator or reducing valve (one of these is 
necessary to reduce the pressure of the gas and 
provide a convenient means of attaching the 
rubber tubing), is made entirely by mechanical 
means, and all daubing of the screw threads 
with soap, grease, red-lead, etc., must be strictly 
avoided; accidents have been caused in this 
way. The stem E of the regulator or reducing 
valve is itself threaded, and has an adapter F 
upon it. Screw this adapter close to the 
shoulder G of the fitting; without any rela- 


157 


Cylindroscope 


tive movement between stem and adapter, 
screw the latter into the cylinder valve; in 
this way the cone on the end of the stem will go 
home into theinverted cone D of the valve. When 
it can go no further, it may be found necessary 
to undo the fitting by, say, the third of a turn, 
and then screw the adapter in as far as it will 
go. Cylinders and fittings for oxygen are 
frequently painted black, and for hydrogen red; 
on the former the screw threads are right- 
handed, and on the latter left-handed. (See also 
* Limelight.’’) 


CYLINDERS, LIME 

Cylindrical pieces of lime, small portions of 
the surface of which are heated to brilliant in- 
candescence by a flame supplied with oxygen 
under pressure. Limes are sold packed in tins, 
but those put up singly in sealed glass tubes 
are the most generally convenient. They 
rapidly disintegrate when exposed to air. The 
chief point in their use is to turn them frequently 
to prevent deep pitting. (See also “‘ Limelight.”’) 


CYLINDRICAL PERSPECTIVE 


Photographs taken with cylindrograph or 
other panoramic cameras of the half circle form 


ate said to be in cylindrical perspective. (See 
** Cylindrograph’”’ and ‘‘ Cylindroscope.’’) 
CYLINDROGRAPH  (Fr., Cylindrographe ; 


Ger., Cylindrograph) 

A panoramic camera invented by Captain 
P. Moéssard, in 1889, with which photographs 
embracing an angle of 170° may be taken on 
a celluloid film bent to a semicircle. The film 
holder or dark-slide is flexible, so that it adapts 
itself to the required form when inserted in the 
camera. The lens is made to rotate on a vertical 
axis passing practically through its optical 
centre; while a tube terminating in an upright 
slit near the surface of the film is rigidly attached 
to the lens setting. When a lens is swung on 
its optical centre the image remains stationary ; 
the various portions of the semicircular film 
therefore receive the parts of a continuous 
picture, while the moving slit ensures that only 
that part directly opposite the lens is exposed 
as the latter moves. This form of camera has 
been of much value in photographic surveying, 
for vertical lines may be ruled at regular dis- 
tances apart on the photograph, to indicate the 
relative angular positions of the different objects 
on a horizontal plane; or a glass ruled with 
similar lines can be laid on the photograph for 
the same purpose. To inspect the views in 
correct perspective, an instrument known as 
the cylindroscope (which see) is employed. 

A panoramic camera on much the same 
principle was designed by Marten, of Paris, 
in 1845, for use with curved daguerreotypes. 


CYLINDROSCOPE (Fr., Cylindroscope ; Get., 
Cylindroskop) 

An instrument designed by Captain P. Moés- 
sard for the inspection or exhibition of panoramic 
views obtained with his cylindrograph camera 
(which see). The print is curved to a radius 
agreeing with that occupied by the film in the 
camera, and the point of view is in the centre, 
a suitable eye-lens being used if necessary. 


D 


DAGUERRE, LOUIS JACQUES MANDE 

Born at Cormeilles, a village near Paris, 
November 18, 1789; died July 10, TBEX, 
Inventor of the diorama (1822) and of daguerreo- 
typy (1838). He began his photographic experi- 
ments about 1824 by unsuccessful attempts to 
fix the images in the camera obscura; his 
neglect of his diorama and scene-painting busi- 
mess caused his wife to seek advice with regard 
to his sanity. In December, 1829, he entered 
into partnership with Niepce, who for fifteen 
years had been working on the same subject, 
and who had made some important discoveries 
which he now shared with Daguerre. The two 
worked together up to the time of Niepce’s 
death (1833), when Isidore Niepce took the place 
of his father. Five years after the death of the 
elder Niepce, Daguerre accidentally discovered 
the process which bears his name, and in the 
Same year (1838) made an unsuccessful attempt 
to form a company to work the process. In 
July, 1839, Daguerre divulged his secret and 
published the process at the request and expense 
of the French Government, who awarded him a 
life pension of six thousand francs on the con- 
dition that the process should not be patented ; 
notwithstanding this condition, a patent was 
taken out in England in 1839. Daguerre wrote 
Historique et Description des Procédés du 
Daguerréotype et du Diorama (1839), and Nouveau 
Moyen de Préparer la Couche Sensible des Plaques 
Destinées &@ Recevoir les Images Photographiques 
(1844). 


DAGUERREOTYPE PROCESS 

The earliest commercial photographic process, 
the invention of Louis Jacques Mandé Daguerre, 
By its means a photographic positive image is 
produced on a polished silver surface. It was 
published in France, in July, 1839, and during 
the next twelve years attained great popularity, 
but the introduction of Frederic Scott Archer's 
wet collodion process, in 1848, soon had the 
effect of rendering the older process obsolete, 
and it is now not practised except experi- 
mentally. Being the first in the field, extreme 
interest naturally attaches to it, and it has been 
thought desirable to explain its working in 
detail. 

Daguerre’s process, as slightly modified in 
details by the inventor in the course of its com- 
mercial practice, is the one here described, it 
being impossible in the space at command to 
discuss the many modifications introduced by 
other experimenters during the ten or twelve 
years following 1839, Briefly, a daguerreotype 
photograph is an image formed by mercury 
vapour upon a silver-coated copper plate. The 
process comprises five operations, namely, clean- 
ing and polishing the silvered plate, sensitising, ex- 
posing in the camera, developing, fixing and finish- 


ing. The sheet copper was silvered either elec- 
trically or mechanically. In England, as a rule, 
Sheffield plate was employed, this being made by 
soldering silver to copper to form an ingot and 
then rolling to the required thickness. The most 
perfect polish upon the silvered surface was 
necessary, and to obtain this it was cleaned with 
weak nitric acid and polished with pumice 
powder, tripoli, and olive oil, the final polish 
being applied with buffs made of velvet, the 
plate having been previously heated to drive 
off the oil. For the purpose of heating during 
polishing, the plate was supported upon an iron 
wire frame A, and heated with a spirit lamp. 
It was essential to obtain a high polish, and 
dozens of methods of securing this were sug- 
gested. 

The second operation, sensitising, was modified 
quite a number of times. In Daguerre’s original 
plan the plate was subjected to fumes of iodine, 
until it assumed a definite golden yellow. If the 
action of the iodine was prolonged, a violet 


A. Wire Frame used by Daguerre for Sup- 
porting Silvered Plate While Polishing 


colour was produced, and this was much less 
sensitive to light. Daguerre’s iodising box B 
had double walls. The vessel of iodine H 
had over it a ring supporting a piece of wire 
gauze. The small lid J was in position only 
when the box was not in use. ‘The plate to be 
iodised was attached to the underside of the 
proper lid K; the lid 1 enclosed the whole. The 
sensitising took a long time, as the crystals of 
iodine had to remain in their natural state, and 
must not be heated because of the possibility 
of moisture condensing upon the plate. The 
vapour caused silver iodide to be formed on the 
silver plate, which was then sensitive to light. 
Although Daguerre appeared to be satisfied with 
plates prepared in this way, many other photo- 
gtaphers tried to increase the sensitiveness. God- 
dard, for example, in 1840 exposed the iodised 
plate to the action of bromine vapour, thereby 
forming silver bromide upon the plate in addition 
to the iodide ; and in 1841 Claudet used chlorine 
vapour in the same way; either of these modi- 
fications reduced the exposure by about four- 
fifths. Bingham followed with bromide of lime, 
which for a time was widely used. These 
accelerators caused the yellow film to assume 


158 


Daguerreotype Process 


other hues, and in each case the plate was put 
back again to the iodine fumes until it assumed 
a rosy hue, 

The third operation was that of exposing the 
plate in a camera (for Daguerre’s instrument, see 
**Camera’’), and, as in the case of modern dry 
plates, the time of exposure depended upon the 
actinic value of the light, etc. Daguerre’s times 
of exposure in Paris, and with plates prepared 
simply with iodine, are said to have been from 
five to thirty minutes; objects in shadow, even 
in the brightest weather, required twenty min- 
utes at least. The daguerreotype plate, how- 
ever, in its modified form needed only from five 
to thirty seconds, according to subject, light, etc. 
It was not an uncommon practice, when 
Daguerre’s original process was used, to whiten 
the face of the sitter by means of powder in 
order to shorten the exposure for the face; 
then, in order to bring out the details of the 
dark objects, such as the dress, a piece of black 
cloth attached to a long stick was held in front 
of the sitter’s face during the time the extra 
exposure was given to the dress. 

An obvious defect in a daguerreotype picture 


de MUU SUE MU LP) @ 
{ V, 


/ 


SN = 


SSNS 


B. Daguerre’s Iodising Box 


taken in an ordinary camera was that the image 
was reversed, exactly as in a ferrotype (or tin- 
type) portrait. To obviate this, it was neces- 
sary to reverse the image by means of a mirror 
attached to the lens, thus increasing the already 
lengthy exposure by about one-third. 

The fourth process was that of development, 
or ‘‘mercurialisation’’ of the image on the 
exposed plate. The latter was taken into the 
dark-room and placed in a dark box C in sucha 
way that the surface was suspended over a 
saucer of mercury heated to a temperature of 
about 140° F. (60° C.). The box had under 
its bottom a lamp M, which heated a dish of 
mercury in which was a thermometer N. ‘The 
plate P, as removed from the camera, was held in 
a grooved blackboard Q, where it could be 
viewed through the glass panel R. The lid of 
the box is shown by s. The fumes of the mer- 
cury “‘developed”’ the image in the course of 
about twenty minutes. The final operation 
consisted in removing the unused iodine from 
the plate of silver in order to prevent the further 
action of light. A saturated solution of common 
salt was first used, and later a weak solution of 
sodium hyposulphite. The developed plate was 


159 


Daguerreotype Process 


placed in filtered rain-water for a second only, 
and then immersed in one of the fixers just 
named until the yellow colour had quite dis- 
appeared; warm distilled, boiled, or filtered 
rain-water was then allowed to run in a stream 
over the plate in order to washit. The shadows 
were represented by the polished surface of the 
silver, and the lights by the adhering and very 
delicate film of mercury, which, if fingered in 
any way, would be wiped off. Therefore, in 
order to preserve the pictures, they were placed 
under glass and the air excluded. In some cases 
the picture was treated with a solution of gold 
and sodium hyposulphite, which brought out the 
details with greater force and brilliancy. ‘This 
idea was originated in 1840 by Fizeau, of Paris, 
who used a solution of 7 grs. of gold chloride in 
10 oz. of distilled water, this being mixed with 
a solution of 30 grs. of sodium hyposulphite in 
4 oz. of water. 

The expense of the silvered plates was a 


C. Daguerre’s Developing or Mercurialising 
Box 


great drawback to the daguerreotype process, 
As late as 1853, the price charged for a 
quarter-plate daguerreotype portrait was fifty 
shillings, and for a half-plate eighty shillings. It 
was the custom to “improve’’ daguerreotype 
pictures by colouring them. Colours ground 
extremely fine were used and dusted on dry 
with a fine camel-hair brush, the process needing 
great care, as it was almost impossible to 
remove any of the colour applied. When the 
colours were on they were breathed upon to 
make them adhere, Claudet’s method was to 
mix the colours with alcohol, and apply cautiously 
with a soft brush, and to dust on dry colours if 
the liquid colours were not dark enough, The 
colours chiefly used were gold, carmine, chrome 
yellow, and ultramarine, by combining which 
any desired tint could be obtained. 
Major-General Waterhouse has found that 
daguerreotype plates can be developed with a 
wet collodion (physical) developer to give a 


Daguerreotypes, Cleaning 


positive image as usual, or with an. alkaline 
developer, or with ferrous oxalate, to give a 
negative image. If before exposure the plates 
are treated with an alcoholic solution of 
erythrosine, they show sensitiveness to the less 
refrangible end of the spectrum. Copper plates 
sensitised with iodine and bromine yield images 
if exposed and developed with ferrous oxalate 
or an alkaline developer, and the results are 
fairly certain. 


DAGUERREOTYPES, 
RESTORING 

Cleaning and restoring a daguerreotype picture 
is at all times a risky process, and should not 
be attempted unless the worker is particularly 
careful and patient. Many methods have been 
advocated, but they all need care and thought, 
and rather than run the risk of ruining a picture 
it is better for the uninitiated to leave the work 
alone. It must be remembered that daguerreo- 
types are valuable relics, and that comparatively 
few modern photographers know how they were 
made. The pictures become indistinct and dull, 
not by fading, as the modern photographer under- 
stands it, but as a result of the oxidising influence 
of the atmosphere, which has been unwittingly 
allowed to act upon them, either because the 
hermetic sealing was imperfectly executed, or 
because it has become broken away. In this 
article is described the method of cleaning and 
restoring that is considered to be the most 
reliable, but before any attempt is made to 
improve the picture the processes by which it 
was produced should be thoroughly under- 
stood (see “‘ Daguerreotype Process’’), the res- 
torer will then know the composition of the 
photograph. This photograph consists of a most 
delicate film on the surface of a silvered plate, 
not varnished or protected in any way, and 
susceptible of injury from any rubbing or 
abrasion. Flicking off the dust with a silk 
handkerchief, or lightly touching the surface 
with the finger or a camel-hair brush, may ruin 
the picture. The operator must first try to 
ascertain whether the picture is in its original 
state, and whether there has been an earlier 
attempt to clean or restore it, because should 
certain chemicals have been left in the film 
the picture may be ruined when others are 
applied. 

The usual and best method of restoring a faded 
or discoloured daguerreotype is as follows: 
Take out the plate from the frame and immerse 
the discoloured picture in a 1 per cent. solution 
of potassium {cyanide in distilled water, care- 
fully rocking the dish until the milky or smoky 
appearance caused by oxidation disappears. If 
the cyanide solution is not strong enough it 
may be strengthened, but particular care must 
be taken to use the purest of distilled water, 
and not to touch the picture with any solid 
substance, even with cotton-wool. As soon as 
the discoloration (oxidation) has vanished, the 
plate must be gently but thoroughly washed in 
several changes of distilled water, avoiding 
ordinary water. Finally, it is dried by gentle 
heat in an atmosphere as free from dust as 
possible, and in nine cases out of ten the simple 
treatment will have restored the picture and 
made it almost, if not quite, as good as new. 


CLEANING AND 


160 Daguerreotypes, Electrotyping 


If, however, the restored picture lacks brilliance 
and detail, it may be redeveloped, but as the 
latter process is particularly risky it should be 
attempted only in extreme and very bad cases. 
Redevelopment is done by exposure to the 
fumes of mercury, and not by the application of 
any liquid. Procure an air-tight box about 
3 ft. high; at the bottom place a small spirit 
lamp, and over it a saucer of pure metallic 
mercury. Carefully fix the plate to be redevel- 
oped to the lid of the box in such a way that the 
picture is face downwards when the box is closed. 
Close the box so that the picture may be exposed. 
to the fumes of the mercury, and examine every 
minute to see how development progresses. 
When all detail is restored, remove the plate. 
Care must be taken during this process not to 
inhale the fumes, as they are poisonous. Tay 
the redeveloped plate on a piece of clean, clear 
glass, and bind the edges with silk strips, using 
Canada balsam as an adhesive; this binding 
must be done thoroughly in order to exclude 
the air. Redevelopment is rarely necessary, and 
is to be avoided on account of the risk to both 
plate and operator. 


DAGUERREOTYPES, COPYING 
Daguertreotypes are difficult to copy satis- 
factorily because of the character of the image 
and the presence of the silvered plate. They 
must be illuminated by a strong sidelight, all 


other light being cut off, and the surroundings 


should be dead black, in order to prevent reflec- 


iv 


| 


ll 


Method of Copying Daguerreotype 


tions. Professional copyists place the daguerreo- 
type picture inside a deep box lined with velvet, 


black cloth, or painted a dead black, with a hole 


cut in one end, through which the camera lens 
peeps. At the end nearest the picture, part of 
the side of the box is cut away in order to admit 
the sidelight, which light should preferably be 
strong sunlight. As a general rule, the picture 
should lie on its side, with its top edge facing 
the direction of the light, because the marks of 
the buffer sometimes show upon the original 
picture, and as these lines run from top to bottom 
they would be accentuated by a light striking 
them at right angles. Focusing, stop, expo- 
sute, plate, etc., are the same as for ordinary 
copying, the whole secret of daguerreotype 
copying being in the arrangement of lighting. 


DAGUERREOTYPES, ELECTROTYPING 
(Fr., Electrotypage des daguerréotypes ; 

Ger., Galvanoplastik der Daguerreotypen) 

The daguerreotype plate to be.electrotyped is 
immersed in an acidified copper sulphate solu- 
tion, as employed by electrotypers, and is con- 
nected by means of copper wires to an electric 
battery or other source of current. A sheet of 
soft copper is placed in the solution to form 
the anode, this being also connected to the 


By A. H. BLAKE, M.A. 
NIGHT PHOTOGRAPHY 


Daguerreotypes, Etching 


battery. A fine coating of copper is thus gradu- 
ally deposited on the daguerreotype, but the 
relief obtained is naturally very slight. 


DAGUERREOTYPES, ETCHING  (Fr., 
Gravure des daguerréotypes a& Vacide 
chlorhydrique ; Ger., Aetzen der Daguerreo- 
typen) 

A process for obtaining intaglio plates from 
daguerreotypes, suitable for photogravure print 
ing, was introduced in 1840 by Sir W. R. Grove 
the inventor of the Grove cell. The daguerreo. 
type was immersed in a solution of one part of 
hydrochloric acid to two parts of water, and 
attached to a wire from the battery, which 
consisted of a pair of Grove cells. Opposite the 
daguerreotype, and about 2 in. away from it, 
was placed a platinum plate connected with the 
other pole of the battery. On the passage of 
the current, an oxychloride of silver was formed, 
and at the expiration of about thirty seconds 
the etching was complete. The oxychloride 
having been removed, the plate was ready for 
printing from in an ordinary press. ‘The results 
obtained were, however, too shallow for anything 
but very delicate work, and proved unsuitable 
for commercial use. In 1843 A. J. F. Claudet 
patented a method of etching the daguerreotype 
plate with acid, but the specification is by no 
means clear. 


DALLAS RUBBER-TYPE 


An invention of Duncan C. Dallas, comprising 
the making of a swelled gelatine relief, and from 
it a plaster cast, the cast forming the mould for 
a vulcanised indiarubber cast to be used as a 
stamp, or in a press. 


DALLASTINT, DALLASTYPE, ETC. 

Duncan C. Dallas was the inventor of a num- 
ber of processes based on the swelling of gela- 
tine, when sensitised with bichromate and 
exposed to light. Dallastint was a process in 
which the half-tones of a photograph were repro- 
duced by causing the gelatine to reticulate into 
a grain resembling that produced in the collo- 
type plate. The effect was similar to that of 
aquatint, and it was eapable of rendering fine 
detail and delicate gradation of tone. However, 
the process never came into practical use, and 
the details were kept secret. The inventor 
claimed that the process could also be used for 
decorative purposes by transfer to pottery, 
stone, wood, etc., and for printing on calico, 
linen, and other textile fabrics. 

Chromo-Dallastint was an adaptation of the 
Dallastint process to colour printing by making 
blocks for each colour. 

Dallastype was a process proposed for making 
relief blocks for typographic printing. The 
inventor made half-tone blocks, and used a ruled 
screen instead of, or sometimes in combination 
with, his reticulated grain. The blocks were 
made of type metal, evidently cast in plaster 
moulds taken from the gelatine relief. 


DALLMEYER, JOHN HENRY 
J. H. Dallmeyer (born 1830, at Loxten, near 
Versmold, Prussia; died off the coast of New 
Zealand, 1883) came to England in 1851 and 
entered the workshop of W. Hewitt, optician, 
li 


161 


Damp, Precautions Against 


afterwards working for Andrew Ross. He 
started in business for himself in 1859, and in 
1862 came to the front as a manufacturer of 
photographic lenses. He made many improve- 
ments in telescopes, and patented a single wide- 
angle lens (1864) and a lantern condenser. He 
married Hannah, daughter of Andrew Ross, 
was elected F.R.A.S. in 1861, and retired from 
active work in 1880. 


DALLMEYER, THOMAS ROSS 


T. R. Dallmeyer, son of J. H. Dalmeyer, born 
1859; died December 25, 1906. Designed 
many important optical instruments, lenses for 
telephotography being perhaps the most import- 
ant, Among his inventions are a rapid triple 
cemented landscape lens and a rapid rectilinear 
landscape lens. He was a prominent member of 
the Royal Photographic Society, and President 
of that body from 1900 to 1903. 


DALLMEYER - BERGHEIM LENS 
‘“‘Bergheim Lens,’’) 


DAMMAR 


DAMMAR VARNISH 

Gum dammar dissolved in benzole, chloro- 
form or turpentine makes a clear varnish, which 
may be used cold and applied, if necessary, with 
a brush. It is particularly suitable for film 
negatives, transparencies, etc. (For formula, see 
“Crystal Varnish.’’) 


DAMP, PRECAUTIONS AGAINST 

Damp plays havoc with apparatus and sen- 
sitive material, which should always be stored 
in a dry, airy place. Camera bellows become 
mouldy in a damp place, lenses spotty, cameras 
may come to pieces, and dark-slides refuse to fit 
or draw out, and shutters to work. Preventives 
ate obvious. Where possible, it is advisable 
to use, for home-made articles, a glue that has 
been damp-proofed by mixing with it while hot 
one-quarter its bulk of linseed oil, stirring 
rapidly during the addition. The addition of 
1 part of potassium bichromate dissolved in 
the least quantity of water to 6 parts of 
melted glue, made with as little water as possible, 
makes a waterproof cement, which must be 
stored in the dark until required for use. A 
precaution against damp is to have cameras and 
dark-slides brass-bound, Dampness in a dark- 
room may cause the detachment of labels from 
the bottles of chemicals, unless these labels are 
protected by a coat of waterproof varnish 
extending over their edges upon the glass. 

Plates and papers deteriorate quickly if not 
kept dry ; and if damp is suspected they should 
be kept in a cupboard or in drawers, with some 
calcium chloride in a tin, either without a lid 
or with a perforated one; the chemical absorbs 
moisture, and when it becomes wet it may be 
dried on a hot shovel or in an oven and used 
over and over again. 

Damp must also be guarded against while 
printing, as damp paper will probably spoil any 
negative with which it is placed in contact (see 
** Silver Stains”’). When printing is carried out 
in wet weather, and there is a likelihood of the 
paper absorbing moisture, it is advisable to use 


(See 


(See ‘““Gums and Resins.’’) 


Dansac-Chassagne Process 


a pad of waterproof sheeting between the back 
of the paper and the frame back, or pads of 
blotting-paper may be used if dried before a 
fire after taking each print. Such a precaution 
is particularly necessary when P.O.P or platinum 
paper is used; and in very wet weather such 
papers may with advantage be dried before a 
fire previous to printing. 

Carbon paper (tissue) is insensitive when wet 
and sensitive when dry; but it is not generally 
known that the film is insensitive when in a 
state of absolute dryness amounting to complete 
desiccation. 

The walls—plain or papered—of dark-rooms 
or work-rooms where photographic material is 
stored may with advantage be covered with a 
waterproof varnish formed of naphtha and 
Shellac, in the proportion of } lb. of the former 
to 1 quart of the latter. The smell of the 
mixture is unpleasant, but soon wears off, and 
the wall is covered with a hard coating utterly 
impervious to damp, and to which wall-paper 
may, if desired, be attached. 

A wooden erection used as a studio, dark- 
room, or store-room, can be given a waterproof 
coating with tar, which is as effective as, and 
cheaper than, anything else. The following is 
also suitable, and can be applied with a brush: 
equal parts of pitch and resin melted together in 
a bucket over a stove, and then, after removal, 
thinned with petroleum ether or paraffin oil. 
The fire risk in preparing this stuff is considerable, 
and the job should be done in the open air. 


DANSAC-CHASSAGNE COLOUR PRO- 
CESS 

A process of obtaining prints in natural 
colours, which was introduced in 1897, and 
originally said to be based on the selective 
absorption of the silver image for the colours 
used. On critical examination it proved to be 
nothing more than local painting with solutions 
of aniline dyes in albumen. 


DARK-ROOM, OR DEVELOPING CHAM. 
BER (Fr., Laboratoire; Ger., Dunkel- 
zimmer, Dunkelkammer) 

A room or cupboard devoted principally to 
the operation of development, and from which 
all white or actinic light is excluded. Until 
A. J. F. Claudet patented, in the ’forties, the 
use of coloured media, preferably red, the devel- 
oping chamber was really in total darkness ; but 
since then the name of “‘ dark-room”’ has been 
somewhat of a misnomer. 

The old idea that space is unimportant in the 
room used for developing is quite erroneous, 
particularly with respect to efficient ventilation, 
so necessary to the health and comfort of the 
operator. It is obvious, also, that greater con- 
venience is secured when there is plenty of room 
for shelves and benches, and for moving about. 
Daylight, owing to its constant fluctuation, is 
not recommended, and does not add to the 
safety of the developing chamber, since sunshine 
or bright light tends in time to bleach non- 
actinic fabrics and materials, and mischief may 
‘be done before this is noticed. It is preferable 
to block out all daylight and to rely entirely 
on aftificial illumination. It is now realised 
that, provided the colour of the light is carefully 


162 


Dark-room 


chosen to match that region of the spectrum to 
which the particular plate employed is least 
sensitive, a much better illumination is per- 
missible with safety than was at one time 
imagined, so long as the plate is not unneces- 
satily exposed to the direct rays from the lamp. 
The old-style dark-room, where the operator 
fumbled uncertainly in a dim, ruby glimmer, 
knocking over bottles and breaking glass 
measures in his inability to see a foot before him, 
is rapidly giving way to saner arrangements. 
In a properly designed developing chamber 
some means should be adopted for preventing 
the admission of light when the door is opened. 
One way of doing this is to have a double door, 
as indicated in the illustration which shows 
how a room 12 ft. by 8 ft. may be fitted up 
as a dark-room. Another way is to curtain off 
a kind of alcove in front of the door, using a 
heavy opaque material. 

An abundant and pure water supply is an 
important consideration if much work is to be 
done. Iron pipes should be avoided, as rust is 
objectionable in dealing with some sensitive 
surfaces. If a constant supply cannot be had, 
a portable tank with a tap or siphon, or even a 
couple of large pails, may be used. Swing rose 


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Plan of Fitted Dark-room 


taps should be fitted if possible; ordinary taps 
are more troublesome, giving too forcible a jet 
and having a marked tendency to splash. But 
if an ordinary tap is provided as well, for use 
in filling bottles only, added efficiency is gained. 
The more shelves that can be fitted the better. 
Those which will hold the bottles or articles 
most frequently in use should be low down and 
well within reach. A small cupboard, with 
drawers to hold unexposed plates and papers, 
will be found extremely useful. 

When a room cannot be kept permanently 
for developing, a bathroom, or even a cupboard, 
may be adapted temporarily for the purpose. 
If the work is done at night, and no outside 
lamps are near, there will be no need to obscure 
any windows that may be present; otherwise 
a wooden frame may be made to fit closely in 
the opening, and covered with any opaque or 
non-actinic fabric. This is readily removable 
when not in use, and may be replaced in a few 
seconds. Portable dark-rooms of various kinds 
are obtainable, and some of these fold into a very 
small space. (See also ‘‘Dark-room Illumina- 
tion,” ‘‘Dark-room Lamp,’’ “ Dark-room Ven- 
tilation,” ‘‘ Developing Bench,”’ etc.) 


Dark-room Clock 


DARK-ROOM CLOCK (See “Clock, Dark- 
room.,’’) 


DARK-ROOM ILLUMINATION 

The colour of the light used for dark-room illu- 
mination is important, both as regards its purity 
and its general character. For ordinary negative 
work a pure red, that does not allow any blue 
rays to pass, is best, and for bromide printing a 
golden yellow or orange will give sufficient 
safety with comfort in working. For most 
colour-sensitive plates a pure deep red is best ; 
but for some that are very sensitive to red a 
special screen for the dark-room lamp is sold by 
the makers of the plates. For all ordinary plates 
and papers the best method for working satis- 
factorily is to light the dark-room brilliantly, 
sufficiently well for seeing all bottles, measures, 
plate boxes, etc., clearly and distinctly. Unless 
there is sufficient light for working in comfort, 
inferior results are inevitable. The room should 
be lighted well, but the plate should be shielded 
or protected from the direct rays of the lamp, 
both in filling the slides and during develop- 
ment. The plate may be brought near the lamp 


A. Folding 
Candle-lamp 


B. Oil-lamp with 
Outside Wick Adjustment 


for a few seconds, when necessary, for examin- 
ation, but otherwise should be shielded as much 
as possible. It is not necessary to cover the 
dish, as the light reflected from the walls has 
very little power; but the dish should be 2 ft. 
or 3 ft. from the lamp and shielded from the 
direct rays. Artificial light is very much safer 
for dark-room illumination than daylight, and 
should always be used when convenient. 


DARK-ROOM LAMP (Fr., Lampe de labor- 
atoive ; Ger., Dunkelzimmerlampe) 

On the satisfactory working of the dark-room 
lamp depends much of the operator’s comfort 
when developing, while the “safety” of the 
light emitted is an important consideration. 
This is qualified to a great extent by the kind 
of plate or paper that is being used, and its 
particular region of colour sensitiveness. Thus, 
for wet collodion plates an amber-coloured 
glass may be used; for bromide paper, one or 
two thicknesses of yellow fabric; for ordinary 
plates, one thickness of orange fabric and two 
or three thicknesses of yellow, or an amber and 
a ruby glass together; while for orthochromatic 
plates a very deep ruby or a special shade of 
green may be employed. Obviously, therefore, 
the ideal dark-room lamp is one that will permit 


163 


Dark-room Lamp 


the insertion of glasses or fabrics of different 
colours according to the work in hand. With 
transparent glass a good deal of light is often 
wasted ; lamps with fabrics capable of diffusing 
the light, or fitted with sheets of ground glass 
or opal in addition, for the same purpose are 
to be preferred, as the room is then more com- 
fortably and uniformly lighted, and the bench, 
shelves, etc., are more readily perceived. For 
temporary use, as when travelling, a folding 
lamp A burning a candle or night-light is con- 
venient; but for constant work candles are 
troublesome and uncertain. Oil lamps are 
fairly satisfactory, if fitted with the wick adjust- 
ment outside, as in B, and kept scrupulously 
clean; but gas and electricity are the only forms 
of illumination that can really be recommended. 
From the facility with which it may be raised 
or lowered, gas is perhaps the best of all, if 
perfect ventilation is secured ; and a good pattern 
of gas lamp is shown at C. A lamp for use with 
electricity is illustrated at D; hanging electric 
lamps are also obtainable. The worker should 
be warned that many of the red incandescent 
electric bulbs in the market are unsuitable for 


C, Gas-lamp D. Electric-lamp | 


photographic employment, unless masked with 
non-actinic fabric. 

With regard to the ‘‘ safe light’ used in the 
lamp, care must be taken that it is suited to 
the plate. A good way of ascertaining this is 
to place an unexposed plate in the dark-slide, 
with the shutter half-drawn, and to expose it 
close to the lamp for about four minutes. It 
should then be developed, when, if the light is 
unsafe, the exposed half will be fogged, and a 
clear line of demarcation will be evident between 
it and the unexposed portion. The exact 
matching of the light to the plate can only be 
done by photographing the solar spectrum on 
the latter, and noticing the region of the spec- 
trum which has no photographic effect. It is 
then possible to obtain a dark-room light of 
the particular colour, or mixture of colours, to 
which the plate is insensitive, by bringing the 
spectroscope into service. Gelatine films, stained 
with aniline dyes, are much used as safe lights, 
as their colour may be nicely adjusted when 
staining. These require to be kept between 
two plain glass plates in the lamp. Since heat 
is detrimental to the stained gelatine films, 
lamps of special construction are made for use 
with them. Other lamps have glass cells in 
front, which may be filled with potassium 


Dark-room Ventilation 


bichromate solution, or a solution of any 
selected aniline dye. (See also ‘‘ Bichromate 
Lamp.’’) . 


DARK-ROOM VENTILATION (Fr., Ven- 
tilation du _ laboratotre; Ger., Dunkel- 
zimmer-venttilation) 

Adequate ventilation of the developing 
chamber is essential to health. Perhaps the 
simplest means of securing it is by the pro- 
vision of light-traps (which see) at the top and 
bottom of the door, or in any other suitable 
laces. Unless, however, these communicate 
with the outer air, the ventilation obtained will 
scarcely suffice. It is as important to secure 
egress for the foul air as to admit fresh, a fact 
which is often overlooked, and outlets should 
invariably be placed at the top. It is not at 
all uncommon to find smail dark-rooms merely 
provided with ventilation apertures near the 
floor, in which case it is next to impossible for 
the vitiated and heated air in the upper part 
of the room to escape. A light-trapped cowl in 
the roof forms a very efficient outlet, but proper 
attention then requires to be paid to the pro- 
vision of openings for the admission of fresh air 
at or near the bottom of the room: or the cowl 
will merely serve to direct a stream of fresh 
air downwards, and will cause an unpleasant 
draught. It is often found necessary to use an 
external electric fan, either to drive in the fresh 
air or to draw out the foul, but care must be 
taken not to raise dust. Whenever dust is 
found to enter by ventilation openings, muslin 
stretched over a light frame should be inter- 
posed before the aperture. 


DARK-SLIDE, PLATE-HOLDER, OR 
BACK (Fr., Chdssis, Chassis négattf ; 
Ger., Kassette) 

A light-tight case to hold the sensitive plate 
or film, always furnished with a shutter or 
shutters, and made to fit closely at the back of 
the camera, from which it may be withdrawn 
at will. There are several kinds of dark-slides. 
That commonly used with studio cameras has 
a hinged door at the back for the insertion of 
the plate, and some of the larger and better- 
class studio slides have roller shutters instead 
of those that draw out. Field camera dark- 
slides are generally hinged in the middle, and 
open like a book, taking two plates with an 
opaque cardboard or metal separator between 


A. Double Book-form Dark-slide 


them. These A are known as ‘“ double book- 
form ’’ dark-slides. The shutters are usually 
cut across and hinged, so that they will fold over 
the back of the slide when drawn, and be out 


164 - Dark-slide 


of the way. Many hand cameras have solid 
double slides, known as the American pattern, 
with pull-out shutters of ebonite or aluminium. 
These are not always perfectly light-tight, 
especially when they get worn. An improved 
pattern is shown at B. The shutters do not pull 
right out, and particulars of the exposure may 


B. Improved Solid Dark-slide with 
Pull-out Shutters 


be written on them. To insert a plate, a lever 
at the bottom is pressed downward (see illus- 
tration B), and the plate then drops into position, 
the lever returning and securing it. Metal and 
cardboard dark-slides are also made. There 


are many special kinds of slides or adapters, | 


to take film-packs, plates in daylight-loading 
envelopes, etc. Roller slides (which see) are 
intended for use with roll-films, and are furnished 
with a winding key and spools. 

In process work, the dark-slides are essentially 
different from those used in ordinary photography. 
The plate is generally held by means of adjust- 
able bars, the bottom one being placed in a notch 
corresponding to the size of the plate, and the 
top one sliding down to rest on top of the plate 
(see illustration C). The metal catches to pre- 
vent the plate from falling outwards are of 
silver when the slide is used for wet-plate work. 
Sometimes the bottom bar is formed into a 
trough, to catch the silver drainings, and in an 
American dark-slide known as the Benster 
plate-holder a glass trough was let into the 
wooden bar. For half-tone work the dark- 
slides are provided with an additional pair of 


C. Wet-plate Holder for Process Work 


bars to hold the ruled screen, and in some forms 
of holder these bars are adjustable so as to give 
more or less separation of the screen from the 
plate. Most.of these process dark-slides have 
roller shutters. 


Dark-tent 


DARK-TENT 


Used for changing and developing plates. (See 
“Developing Tent.’’) 


DARLOT 


A noted French optician and lens maker, 
who made a speciality of casket lenses, under 
which heading they will be found fully 
described. 


DAVIS FOCUSING SCREEN 

A screen used for high-power work in photo- 
microgtaphy, invented by George E. Davis. It 
is used in place of a glass screen for final focus- 
ing, and consists of a piece of wood, preferably 
mahogany, containing seven holes, any one of 
which can take an “‘ A’ photomicrographic eye- 
piece. 


DAVY, SIR HUMPHRY 

Born at Penzance, December 17, 1778; died 
at Geneva, May 29, 1829. President of the 
Royal Society, 1820; made many important 
chemical discoveries and first decomposed 
chemical compounds by means of electric cur- 
rents, preparing in this way sodium, potassium, 
etc. Assisted Thomas Wedgwood in his experi- 
ments with light upon silver and described them 
in the Journal of the Royal Institution (1802) ; 
in the same year he discovered that silver chloride 
gave better results than silver nitrate in the pre- 
paration of a sensitive surface. He made a 
number of photomicrographs, or macrographs, 
by throwing enlarged images of small objects 
through a solar microscope upon sensitised paper 
_ and white leather, but he failed to fix them. 


DAYLIGHT CARTRIDGES 

This term is applied to spools of flexible film 
used in cameras specially adapted for them. 
The strip of film is attached to a considerably 
longer strip of black paper. The spool is placed 
in position in the camera, and one end of the black 
paper is put through a slot in an empty spool 
and wound taut. The camera is then closed. 
By continuing the winding, the first section of 
the film is brought into position for exposure, 
and the successive sections are in turn wound 
along. A number on the black paper behind 
each section can be observed through an open- 
ing in the back of the camera, thus regulating 
the winding and indicating the number of the 
exposure. When the last section has been 
exposed, the rest of the black paper is wound 
on to the spool to protect the film, and the 
camera can then be opened, the exposed spool 
removed, and a fresh one inserted. The film 
thus exposed may be cut up into sections, or 
developed in the strip either by hand or by 
means of developing machines made specially 
for the purpose. The device is an exceedingly 
convenient and popular one. The smallness and 
lightness of the cartridges as compared with 
plates, and the ease with which successive 
spools may be used are strong points in their 
favour, especially with travellers. 

One precaution in the use of film cartridges 
may be mentioned: care should be taken not 
to allow the black paper to run loose on the 
spool, as this will allow light to creep in at the 
edges. Also, in folding cameras, avoid winding 


165 


Definition 


the film while the camera is closed, as some part 
of the bellows or lens may touch the film and 
cause scratches upon it. 


DAYLIGHT CHANGING 

There are several methods by which plates or 
films may be changed in daylight without the 
necessity of resorting to a dark-room. Some 
that come more or less in this category are 
referred to under the headings ‘ Changing 
Bags,” “Film Pack,’ and ‘‘ Daylight Car- 
tridges.”” In addition to these, there are special 
slides made into which plates or films may be 
inserted singly. A pean form is one in which 
each plate or film is enclosed separately in a 
light-tight envelope. The drawing of the 
shutter of the slide opens the envelope, which is 
again closed as the shutter is pushed in. The 
exposed plate in its envelope may then be 
removed and a fresh one substituted. The 
number of exposures is thus only limited by the 
number of envelopes employed. This permits 
of the provision of plates and films of different 
character, which may be selected as required. 


DAYLIGHT DEVELOPMENT (Fr., Dé- 
veloppement en plein air; Ger., Tageslicht- 
entwickelung) 

At various times many methods have been 
suggested for doing away with the dark-room 
for development, and they may be divided into 
two main types: (1) those depending on the 
use of a light-tight tank with ruby glass sides 
into which the plate and developer are intro- 
duced either in a dark-room or tent, the progress 
of development being observed through the red 
windows; and (2) those in which red or non- 
actinic dye solutions were added to the developer 
so as to protect the plate from daylight. (See 
“Developing Machine,” “‘ Developing Tank,” etc.) 


DAYLIGHT ENLARGING 

The oldest method of enlarging, details being 
published in the Atheneum dated July 9, 
1853. A solar camera (which see) was used by 
the early workers, and enlargements were made 
upon albumen or other sensitive “‘ contact’’ paper. 
Bromide paper, as used to-day for enlarging, was 
not commonly obtainable commercially until 
1879 or 1880, although introduced five years 
eatlier. (For modern methods of daylight en- 
larging, see ‘‘ Enlarging by Daylight.’’) 


DEAD BLACK 
Recipes for dead blacks are given under the 
heading ‘“‘ Blackening Apparatus.” 


DECIGRAMME, DECILITRE, DECIMETRE, 
ETC. (See “ Weights and Measures.’’) 


DECOMPOSITION OF LIGHT (See “Light.’’) 


DEFINITION (Fr., Définition; Ger., Definition) 

The degree of sharpness with which objects 
are rendered by the lens. As a rough standard 
for purposes of comparison, it is generally 
assumed that the allowable “‘ circle of confusion ”’ 
shall be one-hundredth of an inch in diameter 
—that is to say, a circle of that size shall be 
accepted as a satisfactory rendering of what 
should be a point. This only holds good for 


) 
Dekagramme 


contact prints from the negative, as it is obvious 
that any enlargement would increase the error 
proportionately and so bring it above the 
standard limit. Some forms of lenses give a 
curved or saucer-shaped field, so that when the 
centre is sharp the definition falls away towards 
the edges. This defect may be counteracted by 
using a smaller stop. Variation in definition also 
arises from the inability of a lens to bring to a 
focus objects on all planes at the same time. 
Improvement in this direction also is brought 
about by the use of asmall stop. Itis not always 
necessary or even advisable to have equally 
sharp definition in all parts of the subject, and 
judicious selective focusing is frequently of 
great advantage. Some lenses are specially con- 
structed to enable the operator to introduce at 
will any required degree of softness or diffusion 
over the entire area, Such softness of definition 
is often most effective in portraiture and in some 
classes of outdoor work. It is generally out of 
place in architecture, copying, and the rendering 
of subjects for scientific purposes. In such cases 
the standard of critical definition should be one 
two-hundredth of an inch or less, and this stand- 
ard is easily attained by good-class lenses. This 
matter is pursued further in the article appearing 
under the heading “‘ Depth of Definition,” which 
should be read in conjunction with the above. 

When spherical aberration is entirely absent 
the centre of the field will be so sharply defined 
that the most delicate sensitive film is too coarse 
to register the smallest details. The structure 
of the sensitive film varies from that of the 
daguerreotype, which is practically grainless, 
through albumen on glass, collodion, and slow 
gelatine emulsions, until the rapid gelatine 
emulsions which show a granular structure even 
when magnified only a few diameters. (For the 
extent of definition which may be reasonably 
expected from a given type of lens at full aper- 
ture, see ‘‘ Field of Lens.’’) 


DEKAGRAMME (See 
ures.’’) 


DELIQUESCENCE 
Zerfltessung) 

A property by which certain chemical salts, 
etc., absorb moisture and become “ watery ” on 
exposure to the air. Ammonium sulphocyanide 
and potassium carbonate are examples of 
deliquescent bodies. Such chemicals should be 
stored in a bottle tightly corked, or made up 
in solution. (For list of deliquescent substances, 
see ‘Chemicals, Storing.’’) 


DEMENEY CHRONOPHOTOGRAPHE 
(Fr., Chronophotographe Demeney; Ger., 
Demeney Kronophotograph) 

A kinematograph machine introduced in 
October, 1893, by Demeney, and improved 
two months later by the addition of the “ dog” 
or cam motion, which may be described as an 
eccentric roller that pulls down one picture- 
length of film each time it comes round. This 
is the first recorded instance of the employment 
of that now well-known movement in the 
kinematograph. Since then, the chronophoto- 
graphe has been added to and elaborated. (See 
also ‘‘ Kinematograph.”’) 


“Weights and Meas- 


(Fr., Déliquescence ; Ger., 


166 


Density Curve 


DENSITOMETER (Fr., 
Dichtigkettsmesser) 


An apparatus for testing the density of a 
given negative as compared with an average 
or standard negative, and estimating the time 
that will be required for printing. In Daw- 
son’s densitometer, a dense part of the negative 
to be examined is held in front of a suitable 
source of light, and a screen illuminated by the 
light that is transmitted is compared with a 
similar screen receiving light from the same 
source through a diaphragm, the aperture of 
which may be varied. 


DENSITY (Fr., Densité; Ger., Schwarzung) 


The relative weight of silver deposited per 
unit area and expressed mathematically as = — 
log.. T or log.. O, T = transparency and O = 
opacity, or, for convenience in working, it is 
usually taken as = — log.,) T. As defined by 
Hurter and Driffield, the law which would pro- 
duce absolutely true tones would be expressed 
by saying that the quantity of silver reduced on 
the negative is proportional to the logarithm of 
the light intensity. Unfortunately, great con- 
fusion exists generally in the use of the terms 
“‘ density ’’ and ‘‘ opacity,’”’ and the very common 
expression, “‘ a very dense negative,” is a typical 
example, inasmuch as what is really meant is 
a negative with great opacities—that is to say, 
the “‘ opacity ’’ of the silver deposited is so great 
that there is very little transparency. By the 
application of a simple factor, densities can be 
at once converted into the weight of silver per 
unit area. 


DENSITY CALCULATIONS 

In photo-chemical investigations it has been 
found that, assuming that the times of exposure 
can be divided into the four periods of under-, 
correct, over-exposure and reversal, the ratio 
of two densities in the period of under-ex- 
posure are exactly equivalent to the ratios 
of the two exposures, or that the amount of 
silver reduced per unit area is directly propor- 
tionate to the exposure. In the period of 
correct exposure the densities are exactly pro- 
portional to the logarithms of the exposures, 
and this is expressed by the formula— 


D= 7 (log. itis C) 


in which D = the density, y = a constant 
depending on the duration of development, 
It = the product of the intensity of the light 
and time, and C = a constant dependent upon 
the speed of the plate. 

The law connecting density with exposure 
may be calculated by means of the following 
‘formula— 


Opacitémétre; Get., 


D = vlog. .[0—(0—1 8 =] ; 
in which D = density, O = the opacity of the 
plate to the chemically active rays, 8 = a fraction 
the hyperbolic logarithm of which is — a It 


= the exposure, and i = the inertia of the 


plate. 
DENSITY CURVE (See ‘ Plates, Testing.’’) 


Density Measurements 


DENSITY MEASUREMENTS 
The measurements of densities are always 
effected with some form of photometer. 


DENSITY, OR SPECIFIC GRAVITY (See 
“Specific Gravity.’’) 


DENSOGRAPH 


A photometric instrument designed by Dr. 
Goldberg, based on the use of neutral tint 
wedges, for obtaining automatically the charac- 
teristic curve of a plate—that is to say, for 
expressing the relations between the densities 
and their corresponding exposures. 


DEPOSITS ON NEGATIVES AND PRINTS 
Fine granular or chalky deposits, usually 
caused by lime in the tap water used for wash- 
ing. Films allowed to dry with deposit adhering 
will feel rough to the touch, but the printing 
qualities of a negative are but seldom affected. 
Such deposits are best removed by gently wiping 
the surface of the negative, straight from the 
washing water, with a pad of wet cotton-wool. 
Methylated spirit or Baskett’s reducer may be 
lightly applied to remove dried-on deposit. 
The peculiar form of deposit that sometimes 
results from the use of an alum bath is due to 
insufficient washing, either before or after using 
the alum solution, a combination of chemicals 
forming with the alum deposits on, in, or under 
the film. Alum is very dangerous to the life of 
a gelatine film when it becomes mixed with 
certain other chemicals. Fixing baths contain- 
ing alum may be decomposed by the alum and 
form deposits. There is no known method of 
removing deposits caused by alum. If a harden- 
ing bath is necessary, formaline should be used, 
as it does not form a deposit. (See also ‘‘ Black 
Spots ” for a peculiar form of deposit on prints.) 


DEPTH OF DEFINITION, DEPTH OF 
FIELD, AND DEPTH OF FOCUS 

** Depth of field”’ is sometimes used as synony- 
mous with “depth of focus”? and “depth of 
definition,” the third expression more correctly 
indicating what is meant. Theoretically, objects 
on different planes, however small their separa- 
tion, are brought to a focus by the lens at different 

oints. In practice, however, itis found that there 
is a certain range within which objects are ren- 
dered with a satisfactory degree of sharpness. The 
distance between the nearest and the farthest 
sharp object is the depth of definition. The 
two chief factors regulating this are the focal 
length of the lens, and the size of the stop 
employed ; tke shorter the first and the smaller 
the second, the greater is the depth of definition ; 
the longer the focal length and the larger the 


aban the smaller is the depth of definition. * 
bi 


a lens is focused on a very distant object, and 
then slightly racked away from the screen until 
the limit of critical definition in the distance is 
reached, it will then be in the position which 
gives the greatest depth of definition. The 
nearest point showing satisfactory definition 
will vary according to the focal length and the 
stop, as already stated. The rule for finding the 
exact distance (known as the hyperfocal dis- 
tance) on which to focus to secure this greatest 
depth, is as follows: Square the focal length 


167 


Depth of Tone 


of the lens (in inches), multiply by roo, and 
divide by the f number. The answer gives the 
hyperfocal distance (in inches). Halving this 
distance gives the nearest point of critical 
definition. 

When a nearer object is focused upon there 
is a certain distance both before and behind it 
within which the definition is also up to the 
standard laid down. The amount of this depth 
for any distance, lens, and stop, may also be 
calculated. Let H be the hyperfocal distance 
(inches) for the given lens and stop, D the dis- 
tance (inches) focused for. The nearest point 
of critical definition is then (H x D) + (H+ D); 
the farthest point is(H x D) + (H —D). The 
range of good definition is always greater beyond 
than before the actual point focused upon. It 
follows that in estimating a distance to which 
the focusing scale is to be adjusted (as in hand- 
camera work) it is better to under-estimate it 
than otherwise. 

A lens is sometimes said to have a deep focus 
when it renders both near and distant objects 
sharply at one time; but as the focus of a 
pencil of rays should be a point, it is evident that 


Diagram Showing, in Exaggerated Form, the 
Effect of Diameter of Aperture on Disc of 
Confusion 


depth of focus is, strictly speaking, non-existent. 
In practice it is convenient to assume that an 
image composed of discs of confusion not more 
than ‘oI in, in diameter is ““sharp’’; so that in 
this case the depth of definition is the distance 
before or behind the true focal plane between 
which the plate intercepts a cone of rays (of 
which the lens diaphragm is the base) at less 
than the diameter above named (-o1 in.). It 
thus follows that the larger the working aper- 
ture the less the depth of definition, as indicated 
in the diagram, in which A is the cone of rays 
from a small aperture, B the cone from a larger 
one, and c and bp the diameters of the discs of 
confusion respectively formed; the more acute 
the angle, the smaller is the disc. The surface 
of the sensitive film is indicated by the line k. 
By halving the diameter of the aperture the 
depth of definition is doubled, and so on in the 
same proportion. It also varies inversely as 
the square of the focal length of the lens for 
the same intensity, or inversely as the focal 
length for the same aperture. (See also ‘‘ Hyper- 
focal Distance.’’) 


DEPTH OF TONE 
A term used, somewhat loosely, in pictorial 
photography to describe the lowness of the tone 


Derepas Mounting 


values, and in technical photography to describe 
the extent to which a picture has been toned or 
developed. A print is said to be deep or low 
in tone when, generally intentionally, it has no 
brilliant high lights, and the appearance is dark 
or gloomy. Black or cold tones appear deeper 
than warmer ones; in other words, assuming 
a black-and-white bromide print to be cut into 
two, and one half toned to a brown, the brown, 
as a rule, does not appear so deep in tone as the 
black part. The depth to which a picture is 
toned or developed influences considerably the 
final result. As a consequence of toning gelatino- 
chloride (P.O.P) and other print-out papers, the 
tone becomes less deep, due to (a) the negative 
being flat, foggy, or otherwise unsuitable, (b) 
quick (or surface) toning, in which case the tone 
is on the top and easily taken off by the fixing 
bath, and (c) the use of a “hypo” bath in an 
acid condition. A black-and-white bromide 
print that is not fully developed will lose much 
of its depth of tone in a sulphide toning bath. 


DEREPAS MOUNTING (See ‘Dry Mount- 
ing.’’) 


DEROGY 


A French optician of the ’fifties and early 
’sixties. In 1859, he made public a half-plate 
convertible lens, with combinations fitting 
together by bayonet joints instead of the usual 
screws. Six changes were possible. 


DESICCATED DRY PLATES 

Dried, or heated, dry plates. It is well known 
that dry plates, as ordinarily used, retain a con- 
siderable percentage of water, mainly in mole- 
cular combination with the gelatine. Howard 
Farmer, to whom the idea of desiccated 
plates is due, found that the water has a 
large influence on the image at the time of 
exposure, definition, detail, density, speed, etc., 
being affected. He found, moreover, that very 
small differences in the percentages materially 
affect the result, so that negatives vary with 
the atmospheric conditions, as to temperature 
and humidity, at the timeof exposure. Accord- 
ing to Farmer, “The drier the film, the 
better the definition, and the greater the power 
of rendering fine detail; in lesser degree, the 
greater the speed and facility of developing 
density. This property of the film can be 
utilised by desiccating dry plates for work where 
definition, detail, brilliancy, or maximum speed 
are desired, and in exposing plates wet where 
softness of image or the destruction of small 
textures and details are sought for. Extra 
rapid and orthochromatic plates, in which the 
former of these qualities is usually found 
lacking, gain them when desiccated to an extent 
hitherto only found in wet collodion or other 
specially prepared films.” 

A perfectly flat-topped kettle containing boil- 
ing water is a convenient appliance for desiccating 
plates; these are simply laid film side upwards 
on the kettle top with a piece of bibulous paper 
between to equalise the heating, and kept there 
for a few minutes at a temperature of 200° F. 
(about 93° C.) before being placed in the dark- 
slides. Or a thick copper slab with an asbestos 
cover can be used. Too great or too prolonged 
heating will crack the dry plate or induce fog. 


168 


Detective Camera 


Desiccation must be carried out in a dark-room, 
and the plates should be exposed while hot 
or as soon after the treatment as possible. 

In process work, desiccated dry plates have 
been recommended for direct colour work. 


DETACHABLE FRONT (Fr., Planchette se 
détachant ; Ger., Objektivbrett) 

A panel holding the lens and made to slip 
into a rebated opening in the camera front, in 
which it is secured by turn-buttons. It may 
be either square or circular. Any number of 
lenses, of different sizes, can thus be used on 


Square Detachable Front 


the same camera, a separate front being provided 
for each lens. For temporary use with a strange 
lens, when a panel is not forthcoming, a piece of 


stout cardboard may be cut to fit the opening . 


in the camera front, a circular aperture being 
made in this to fit tightly on the lens. The 
inner side of the cardboard should be blackened. 


DETAIL (Fr., Détail ; Ger., Einzelheit) 

The clear rendering of detail is largely depend- 
ent on focusing, and the defining power of the 
lens. A tree may be so rendered as to appear 
as a more or less homogeneous mass, or so as 
to indicate its leafy detail. The degree to which 
detail should be shown depends upon circum- 
stances; in some cases the most minute details 
require to be clearly shown, and in others such 
a rendering is far from satisfactory. Suppres- 
sion of detail results in the quality known as 
“breadth,” but over-suppression leads to a loss 
of “ texture.”” For example, a wicker-work bas- 
ket showing every detail clearly would probably 
look hard and “fidgety’’; on the other hand, 
the detail might be so suppressed as to make 
it difficult to recognise that the basket was of 
wicker-work at all. The direction and strength 
of the light and the state of the atmosphere 
are important considerations. 


DETECTIVE CAMERA (Fr., Chambre détec- 
tive ; Ger., Detectiv-Kamera) 


A term that appears to have been invented 
by T. Bolas, who in 1881 described a twin-lens 
magazine hand camera with focusing adjust- 
ment and pneumatic release, and having a 
reversing prism placed before the lens, so that 
the apparatus need not be directed at the 
person to be taken, who would remain quite 
unsuspicious of being photographed. Later, the 
name was applied loosely and inappropriately 


Deterioration 


to all box-form magazine hand cameras, which 
are still so designated in France. Practically 
the only cameras likely to be of real service in 
the detection of crime are those which are either 
entirely disguised, or are worked from a dis- 
tance by the aid of a telephotographic lens. 
(See also ‘‘ Disguising the Camera.’’) 


DETERIORATION 

Lenses, chemicals, and sensitive plates and 
papers all deteriorate more or less according to 
the length of time and manner in which they 
are kept. The commonest form of lens deterior- 
ation is due to the gradual depolishing of the 
glass surface by dust, the action being assisted 
by the careless or rough use of the dusting cloth. 
It is better to remove dust by blowing it off, but 
if wiping is necessary it must be done carefully 
(see “ Lenses, Cleaning ’’). Sometimes when a 
lens is put on one side for a time an iridescence 
spreads over its surface, due to dampness. 
Lenses stored in a strong light often become 
slower in action, because of the yellowing action 
of light upon the balsam with which the lens 
glasses are cemented together. 

Dry plates and sensitive papers deteriorate 
very quickly if not properly stored in a dry, 
airy place, the worst place being a high shelf 
where gas fumes can get to them. The effect 
of age on a plate much resembles that of a very 
slight exposure to light; but dry plates keep 
remarkably well if stored carefully, and skilled 
wotkers can frequently get good results on 
plates as old as twenty years. 

J. B. B. Wellington in 1905 pointed out 
that the popular sulphide toning bath has a 
deteriorating effect upon plates and papers; 
everyone knows that the minute quantities of 
sulphur contained in a London fog will tarnish 
silver articles, producing upon them a thin film 
of silver sulphide, and that the sulphur in 
coal gas has the same effect when the gas is 
burnt. It is thus easy to understand how much 
more deleterious must be the large quantities of 
sulphur given off from the sulphurising bath of 
sodium sulphide on the still more delicate silver 
bromide and silver chloride which go to make 
up the emulsions coated upon plates, films, 
papers, etc. When these are kept in a room in 
which sodium sulphide is employed, they will 
become unusable in the course of a few weeks. 


I II 
Pyrocatechin + caustic soda . ‘ I5 | 100 
Metol + potassium carbonate . ; 20 75 
Hydroquinone + caustic potash. ; 25 60 
Amidol . , : 30 50 
Adurol + potassium carbonate . 30 50 
Paramidophenol ++ potassium carbonate 40 38 
Rodinal ; ‘ 40 38 
Pyro + potassium carbonate , : 40 38 
Glycine + caustic soda. : 45 33 
Eikonogen + potassium carbonate ‘ 50 30 
Pyrocatechin + potassium carbonate . 60 25 
Hydroquinone + potassium carbonate 70 21 
Diphenal . - 75 20 
Glycine + potassium ‘carbonate . vale 95 20 
Ferrous oxalate : : : 75 20 


Diogen ++ potassium carbonate “ ‘ 95 16 
p> | 


169 


Developer 


Plates affected by sulphur will develop with an 
iridescent stain, with general deterioration and 
fog. Bromide and gaslight papers are affected 
in practically the same way, producing a flat 
and dirty print. With P.O.P. the surface will 
assume a metallic lustre, and when printed will 
be difficult to tone. Self-toning papers appear 
to discolour more quickly than other papers, 
but frequently this defect disappears in fixing. 


DEVELOPER (Fr., Révélateur; Ger., Ent- 
wickler) 


Any agent used to render visible the latent 
image, or, in other words, to reduce to silver or 
other metal the latent image produced by the 
action of light upon any sensitive salt. In 
ordinary photographic phraseology the term is 
applied to the solutions generally; whereas 
strictly speaking it should be applied only to 
that chemical or agent which actually reduces 
the exposed silver salt. « 

The composition of the developing solutions 
varies considerably not only with each make of 
plates, but frequently with each worker; but 
there is a definite quantity of developing agent 
which should at least be used, and this is un- 
doubtedly largely dependent on the number of 
molecules in the active group, and the amido 
groups are more active than the hydroxyl 
groups. Von Hiibl has given the following table 
based on this fact, which shows the best con- 
centration of the actual developing agent and 
also the strength usually employed, assuming 
that a 5 per cent. solution of potassium carbon- 
ate is used as the alkali. 


Weight in every 100 parts of 


developer 
Calculated Generally used 
Metol . C0 0-6 
Pyrocatechin | - 06 0:6 
Hydroquinone 06 O*5—I°O 
Amidol Q O*4 0-4—0'8 
Paramidophenol Ors 0°4—0'7 
Pyrogallol O°5 0*3—0°6 
Eikonogen o'9 O-8—1°5 
Adurol . I°O I-O 
Diogen . . te ee I°2 
Glycine 0? 5— Io 1°O 


The calculated quantities will give the maximum 
rapidity of development. 


III IV V VI VII Vil 
0-6 5 Io 20 slight 03 
0°8 5 Io fe) very slight 0°5 
I°O IIo 105 70 slight O°4 
O°4 50 60 5 considerable — 
0°6 30 45 25 considerable 0-6 
0°5 70 30 30 considerable 0O°5 
0°5 45 40 30 slight o°9 
O'5 35 55 40 considerable 03 
0-6 go POT | S25 slight 08 
o°5 85 55 80 slight 0-6 
O°5 I40 60 70 | very considerable | 0°6 
O-7 95 80 120 slight O04 
0:8 30 80 25 slight o-7 
O'5 210 130 115 | very considerable | 1-0 
o°5 280 rere) 80 slight | o8 
0°4 II5 120 80 considerable ais O-7 


Developer, Viscous 


A second table, also due to Von Hiibl, is that at 
the foot of the preceding page. In column I. is 
given the duration of development to yield a cer- 
tain density, in column II. the relative rapidity of 
development, in column III. the relative density- 
giving power, in column IV. the slowing of 
development in seconds by the addition of 
2 per cent. of potassium bromide, in column V. 
the retardation in seconds due to cooling the 
developer to 50° F., in column VI. the retarda- 
tion in seconds by diluting with an equal volume 
of water, in column VII. the action of bromide 
on the density, and in column VIII. the keeping 
power of the mixed developer, 1 being taken as 
that which keeps longest. 

A developing solution should contain a certain 
quantity of alkali to form the actual developing 
salt or to increase the reducing power of the 
developer proper ; and for this reason it is called 
the accelerator. A preservative is required to 
prevent too rapid oxidation or the deposition 
of an organic stain due to the oxidation of the 
developing agent. 

The alkalis generally used are sodium car- 
bonate, potassium carbonate, and caustic soda 
and caustic potash. Some alkalis act better 
than others with given agents, and on the Euro- 
pean Continent potassium carbonate is generally 
used, whilst in England the corresponding 
sodium salt is used. The preservative is usually 
sodium sulphite, whilst potassium metabisulphite 
is occasionally used also. Only a few years ago 
an alkaline bromide was recommended in almost 
all cases, but this was partly due to the fact that 
the plates then did not work quite free from fog. 
Of late years the use of bromide has become much 
less general. Formule for the various developing 
agents are given under the respective chemicals. 


DEVELOPER, VISCOUS (See 
Developer.’’) 


DEVELOPERS, COMPARATIVE COST OF 

The prices given below are approximate for 
each working quart (40 oz.) of developer at 
normal strength as prepared for pouring upon 
the exposed plate. The chemicals are taken at 
British retail prices. 


** Viscous 


O Ps. 


Adurol (one solution) 
Adurol (two solutions) . 
Amidol : ‘ ‘ 
Edinol ‘ : 
Hikonogen (one solution) 
Hikonogen (two solutions) 
Ferrous oxalate . : 
Glycine (one solution) . 
Glycine (two solutions). 
Hydroquinone ; 
Hydroquinone-metol , 
Imogen sulphite . 
Kachin (one solution) . 


ONMWO COAW 
res) 


Le 


Pyrocatechin (one solution) . 
Pyrocatechin (two solutions) 
Rodinal : 


Metol-hydroquinone, according to one maker’s 


COSCOOHOHODODOCOOH OH OMe 
N 
we 


Kachin (two solutions) fe) 
Metol . ‘ ‘ : IO 
Ortol . ‘ : ‘ I 
Pyto-soda . ; : 5 
Pyro-metol . 6 
4 
9 
7 


170 


Developers, Mixed 


formula, costs 1od. per quart, and according 
to another maker’s only 53d. In actual ptac- 
tice, and on the basis of developing a fixed num- 
ber of plates, there is not much difference, 
as manly of the more expensive solutions are 
capable of treating a far greater number of 
plates than the cheaper ones, bulk for bulk. 


DEVELOPERS, MIXED OR COMBINED 

Mixed developers—as, for example, hydro- 
quinone and metol—have become popular. 
Developers are of two distinct kinds: (1) those 
that give detail quickly and density afterwards ; 
these include metol, rodinal, etc; (2) those that 
give density first and detail gradually—for 
example, hydroquinone and pyro. Taking one 
of each class and blending, it is possible to obtain 
a combination of characteristics; thus metol 
with hydroquinone gives detail without excessive 
thinness of the image or duration of development. 
The most is obtained with a combined developer 
by compounding it from one having a low 
factor number (see “ Development, Factorial ’’) 
with one of a high factor; and while most 
developers may be mixed together, there is no 
advantage in combining two developers of 
practically the same factor numbers, as, for 
instance, pyro and hydroquinone, both of which 
may be said to have, roughly, the factor of 6. 
A better combination is hydroquinone (factor 6) 
and metol (factor 30). 

The best known and most widely used com- 
binations are hydroquinone and metol, and pyro 
and metol, but the following have also their 
advocates: Metol-adurol, hydroquinone-eikono- 
gen, hydroquinone-pyrocatechin, hydroquinone- 
rodinal, hydroquinone-amidol, metol-glycin, and 
others. Formule for some of the best known 
mixtures are :— 


Hydroquinone-Metol 


Metol ; 33 gts. 3°4 g. 
Sodium sulphite 90°: 10*2-,, 
Hydroquinone os Ag 
Potassium carbonate . 198 ,, by Pies 
Water to 20 Oz, 1,000 ccs. 


The above is a one-solution developer, ready 


for use. (See also “ Metol-Hydroquinone,’’) 
Pyro-Metol 
A. Pyrogallic acid 55 gts. 5°5 g. 
Metol . : : 3 adh 
Potassium metabi- 

sulphite . Poe fog pee 

Potassium bromide 20 ,, > A 
Water (boiled) to 200z 1,000 ccs 

B. Sodium carbonate 

(crystals) . Mey as 200 g. 

Water (boiled) to 20 ,, 1,000 ccs, 
Use equal parts of A and B. 
Etkonogen-Hydroquinone 

A. Hydroquinone 40 gts. 4 g. 

Hikonogen . hogs 124, 

Sodium sulphite I Oz. Scie 

Citric acid 20 grs. a 
Water to 20 OZ, 1,000 CCS» 

B. Sodium carbonate 60 grs, 6 g. 

Sodium hydrate . 32 ,, Lup eh 

Potassium bromide 6 ,, Gi. 
Water to. - 2002, 1,000 ces, 


Mix A and B in equal parts. 


Developers, Mixed 


Metol-Glycine 


Glycine j . 50 gers. See, 
Metol ‘ : Bae Ls he Fy Br 
Sodium sulphite 21 OZ. roe 
Potassium carbonate . 2} ,, Log) 4 
Water to . ; 4 ee 1,000 ccs. 
One solution, ready for use. 
Edinol-Hydroquinone 

Water to : 20 OZ, 1,000 ccs. 
Acetone sulphite 75 grs. 7th 2. 
Sodium sulphite I OZ. i Mt 
Edinol 30 grs. 74) 
Hydroquinone eo hd hag 
Potassium carbonate 2 OZ. 100 


”) 

Dissolve in the order named, and for over- 
exposure add one drop of a 10 per cent. solution 
of potassium bromide to each ounce of developer 
used. The above is a one-solution, ready for use, 


Hydroquinone-Rodinal 


A. Hydroquinone . 120 grs. 136 g 
Sodium sulphite I OZ, 54°5 5, 
Citric acid ec. Sy See ik 
Potassium bromide 60 ,, Cac. 
Water to ia. CHE. 1,000 ccs 

B. Potassium carbonate 2 ,, 100 g 
Rodinal A AS Sale Bole hy 
Water to. I a 1,000 ccs. 


For soft negatives use equal parts of A and B 
and water. For brilliant and harder negatives 
use equal parts of A and B without water. For 
detail increase the proportion of B, and for 
density increase that of A. ; 


Pyro-Amidol 


Sodium sulphite . 198 grs. 20 g. 
Sodium carbonate ee AI as 6:6 ,, 
Pyrogallic acid :. ey » He 
Amidol 3 ‘ pal ts ee Gia a 
Water to 20 OZ. 1,000 ccs. 


Add the amidol just before developer is required, 
and it will be ready for use. It will not keep. 


A durol-Metol 


Metol ; . 118 grs, 13°5 g. 
Adurol , : ALG, Ae 
Sodium sulphite 7 OZ. Le 
Potassium carbonate . 4°7 ,, 256, 
Potassium bromide 21 gts. 2thas, 
Water to 20 OZ. 1,000 ccs. 


Dissolve the chemicals in the water in the order 
named. To develop plates add 1 part of the 
above to 2 parts of water. 


Pyrvo-Hydroquinone 
This is a mixed developer sometimes advo- 
cated, but both agents being slow-acting and 
somewhat alike, it is mot particularly advan- 
tageous. It is included here chiefly because 
of the boric acid in the formula :— 


A. Hydroquinone 8 grs, "as or. 
Pyrogallic acid . 80 ,, 8 
Potassium metabi- 


sulphite . nS! ys Sy, 

Boric acid (crystals) 10 ,, rm; 
Water . . « "ROOK 1,000 ccs 

B. Sodium sulphite . I ,, 50 g. 

Sodium carbonate EP 50, 
Water . . sa CE gg 1,000 ccs. 


171 Developing 


The boric acid is used as a restrainer because of 
its remarkable corrective power in cases of over- 
exposure. 

A mixture of hydroquinone and eikonogen was 
introduced in 1892 under the name of ‘* Mixtol.”’ 
The formula is :— 


Sodium sulphite . 924 gts. g2 g. 
Hydroquinone . 9 4 ee 8. 
Hikonogen . AIT, as Doss 
Potass. ferricyanide .154 ,, ee 
Potassium carbonate . 577 ,, GDS ee 
Caustic potash . iE EG 5d insog 
Potassium bromide . 8 ,, Cee 
Boiling water 18 0Z. —_—_ 1,000 ccs, 
Glycerine to 5 mins. Rr a 


Mix in the order named, allowing each to dis- 
solve before adding the next. The solution is 
of a yellowish colour, and keeps well. For 
‘“‘instantaneous’’ work, add one-half water; 
for time exposures, two-thirds, or omit the 
caustic potash and increase the carbonate to 
700 grs., and add more bromide if necessary. 
It may be used over and over again, and it is 
claimed not to stain or frill. 

A mixture of rodinal, hydroquinone, and 
eikonogen, known as “ Cyclol,’”’ was at one time 


popular. The formula is :— 
Fikonogen . 100 gts. IO g. 
Hydroquinone . Fs eee ae 
Rodinal : 9 drms. pte 
Sodium sulphite 24 OZ. 13%, 
Potassium carbonate . 2} ,, 12505 
Water to ; ie BO ler SOOT ACG, 


The above is a stock solution. For use in 
warm weather, 1 part is mixed with 7 parts of 
water; in cold weather, less water is used; 
and in very cold weather, only 3 parts of 
water. 

Two developers are sometimes used separately 
instead of mixing, but they have no advantages 
over the combined developers given above. 
Detail is first secured with a quick-working 
developer and density afterwards obtained with 
a slower-working one. The following is an 
example: Develop with rodinal of ordinary 
developing strength until all detail has been 
brought out; then finish with ordinary pyro- 
soda developer, or preferably with the following 
one-solution mixture of hydroquinone :— 


Hydroquinone « £20 prs. I2 g. 
Sodium sulphite I OZ. 50 ,, 
Potassium carbonate . I},, 88 ,, 
Water to . > ke sie 1,000 ccs. 


DEVELOPING 

This article will be devoted to a simple ex- 
planation of the ordinary method and practice 
of developing a dry plate. The exposure having 
been made, the closed dark-slide is removed to 
the dark-room, and the plate developed either 
at once or at any convenient time afterwards. 
The work must be done in a safe light. In 
front of the lamp place a cleaned earthenware 
developing dish of the required size, and near 
it a glass measure containing about 2 oz. of the 
developer. Into another dish pour some fixing 
solution, made by dissolving 4 oz. of sodium 
hyposulphite (“‘hypo’’) in 20 oz, of water. 


Developing 


As all photographic solutions work more 
slowly when cold, it is advisable to mix up all 
solutions some time before they are needed, as 
when freshly mixed they are very cold, particu- 
larly the “hypo” solution, which drops almost 
to freezing point. when newly mixed. By stand- 
ing some time, the solutions become of the same 
temperature as the room. Anything between 
65° and 70° F. (18° and 21° C.) is the best for 
developing and fixing solutions. 

The beginner is recommended to use the hydro- 
quinone-metol developer (see ‘ Developers, 
Mixed ’’), and he should be informed that each 
chemical in the formula plays its own part. 
Hydroquinone and metol are the developers 
proper; but they need the help of the other 
ingredients. Hydroquinone gives density, and 
‘metol detail; so by combining the two, density 
and detail are obtained at the same time. The 
sodium sulphite is included to preserve the solu- 
tion, and is called the preservative. The sodium 
carbonate or potassium carbonate quickens the 
developing action, and is called the accelerator. 
Potassium bromide is frequently added, and 
this controls the action, and keeps the negative 
clear. As each has its own characteristic action, 
it will be obvious that were the chemicals in 
separate solutions, they could be so adapted, if 
necessary, to suit under- or over-exposure; but 
there is no need to trouble with separate solu- 


tions. A good mixture is given below: 
Hydroquinone . -/ 30-9%8 7S. 
Metol : ; oe pes aie 
Sodium sulphite 35s $0 :,, 
Sodium carbonate . 350 ,.- 18 Ree 
Potassium bromide . 5 ,, ro oe 
Water to. . oe NIOROL, 1,000 ccs. 


Take particular care that no stray light enters 
the room, and that the only illumination comes 
from the red lamp. Remove the exposed plate 
from the slide and look at it, but not too near 
the lamp. Nothing on it will be seen; it will 
appear exactly as it did before the exposure, The 
image is latent (that is, concealed or hidden), 
and it needs to be brought out by the developer. 
Put the plate in the developing dish, the 
sensitive or creamy side of the plate being 
upwards and the glass side resting on the 
bottom of the dish. Then pour the developer 
over the plate in one quick sweep, so that the 
plate is completely covered in one sharp even flow, 
preferably from one corner. If the developer is 
properly applied, no air bubbles will form; but 
should any appear, break them quickly by touch- 
ing them gently with the finger-tip, or, prefer- 
ably, with a clean camel-hair brush. Then rock 
the dish from side to side and end to end, so that 
the developer flows evenly over the entire plate, 
taking care to expose it to the red light as little 
as possible. The brightest parts of the resultant 
picture, such as the sky, white collars, and white 
dresses, etc., will appear first of all. If the expo- 
sure is a landscape the sky will be the first to 
appear; but it will be black, as all lights and 
shades are reversed in a negative, the black or 
very dark parts of the actual scene appearing as 
almost clear glass and the whites almost or quite 
opaque. After the sky, the half-tones of the 
pictures will appear, and finally the details in 
the shadows. The developing dish must be 


172 


Developing Bench 


gently rocked all the time. When the image has 
appeared, the plate must not be removed, but 
development continued for some little time 
longer, so as to add density to the negative. 
Continue for about a minute or so after the 
density appears to be correct, as this will be 
considerably reduced in the fixing bath. 

It is important to know how long to continue 
development, and some experiments at the cost of 
a few plates will teach more than will many 
pages of printed matter. A negative that is 
taken out of the developer too soon is very thin, 
and will not give a good, clear picture ; whereas a 
negative that has been left in the developer too 
long will be dense or harsh. As a general tule, 
when the negative is sufficiently developed, the 
dark parts in the negative, such as the sky, will 
show through the negative, and can be seen when 
the plate is examined from the glass side. ‘The 


plate may also be taken out of the developer once 


or twice, and examined by holding it up to the 
red lamp, and its density judged by looking 
through it. 

In cases of under-exposure, the image comes 
up very slowly, or only the high lights appear 
and not the half-tones and shadows. Develop- 
ment should be complete in ten minutes or even 
less. If after, say, fifteen minutes nothing, or 
very little, appears on the plate, try breathing 
on it, or warm the developer, but only very little, 
or the film will melt. If after a long time nothing 
appears, the plate may be destroyed as being 
useless. On the other hand, if the image appears 
extremely quickly, and the plate goes black all 
over in a minute or two, the plate has been over- 
exposed, or fogged by light other than that 
through the lens. A little extra potassium 
bromide added to the developer will sometimes 
Save over-exposed plates if it is known that they 
are over-exposed before the developer is poured 
on; but after development has started it is a 
waste of time to add the bromide. 

Subsequent processes, assuming that all has 
gone well, include a minute’s rinsing in cold water, 
and transference, film uppermost, to the fixing 
bath, in which the plate remains for a period 
twice as long as that occupied by the whiteness 
in disappearing. ‘Thus, if the whiteness disap- 
pears in ten minutes, allow the negative to 
remain for a further ten minutes, (See also 
“ Fixing.”) Finally, the negative, which may 
now be brought out into the daylight, is washed 
for at least thirty minutes in running water (see 
also ““ Washing ”’), while it stands on edge. 

The beginner is recommended to adopt the 
factorial system of development. (See ‘De 
velopment, Factorial.’’) 


DEVELOPING AFTER FIXING (See “ Fix- 
ing before Development.”’) 


DEVELOPING BENCH OR _ SINK (Fr., 
Etabli de développement ; Ger., Entwick- 
lungsbank) 


A bench or table specially designed for develop- 
ing, and usually provided with a stoneware or 
leaden sink. The top, if of wood, should be. 
coated with shellac or other waterproof varnish. 
The height should be such that the operator 
can work at it without either stooping or strain- 
ing, and there is no reason why it should not 


Developing Dish 173 


be low enough for the worker to sit at, if this is 
desired. The continuous standing customary is 
merely fatiguing, and in no sense necessary. A 
very slight slope to the sides of the bench, so 
that spilt solutions may run into the sink, is 
useful; but this is often much overdone, so 
that bottles are liable to be upset, and the 
contents of full dishes to escape over one side. 
The developing bench may be either fixed or 
portable, but the essential features are practically 


Developing. Bench 


the same in each case. A typical portable bench 
is illustrated. The sides are grooved so as to 
drain into the sink, which is of vitrified stone- 
wate. The water is supplied by a swing-arm 
tose tap, under which may be placed a loose grid 
to hold dishes, etc. Convenient shelves for 
bottles, and racks for dishes, are fitted. 


DEVELOPING DISH (See “ Baths.’’) 


DEVELOPING FILMS (See “Developing 
Machine,” ‘‘ Film Developing, etc.’’) 


DEVELOPING AND FIXING COMBINED 

A system of developing in which a sufficient 
amount of “hypo” is mixed with the developer 
in order that developing and fixing may be per- 
formed at the same time, a method thought 
much of at one time but little used nowadays. 
The secret of successful work is in the use of the 
correct amount of “‘hypo”’ to balance the 
developer. The “hypo” may be mixed separ- 
ately and added to a developer, or made up in 
the developer itself. For the latter method 
edinol is perhaps the most suitable :— 


Sodium ‘hyposulphite 150 grs. 26 g. 
Sodium carbonate . $ oz. Gag. 
Sodium sulphite . 300 gers. es 
Edinol . ‘ : 4 02, ce 


Dissolve the first three in 12 oz. of water, add 
the edinol, and use at once. The former method 
is to make up the “‘hypo”’ and developer proper 
separately and mix before use, as follows :— 


{ 


Developing Machine 


Ordinary developer. 57 Oz: I50 ccs. 
Sodium hyposulphite sol. (20%) 2 or 3 drops 


The following developer is one that is popular 


upon the Continent, and works well with 
““hypo” :— 
Hydroquinone . 60 gts. 8-5 g 
Metol ‘ : oa MOY Arty 
Sodium sulphite MAB OG 55 64°5 ,, 
Sodium carbonate . 600 ,, obey 
Water to . ; oiei Go oz, 1,000 ccs, 


The “hypo ”’ solution is added in the proportions: 
stated above immediately before use. 

If properly mixed, development is completed. 
at the time the plate is fixed, and the negative’ 
simply requires the usual washing. The method 
forms an interesting experiment, but is not recom- 
mended for valuable exposures, as with some 
plates it does not always work so well as could 
be wished. ‘‘ Hypo” also acts as an acceler- 
ator with some developers. (See ‘‘ Hypo in 
Developer.’’) | 

Kachin is one of the most suitable developers 
for combination with “hypo.” J. McIntosh 
advocates the following :— 


A. Kachin : .. 60: gts. 15°5 g. 
Sodium sulphite . 600 _,, LoS) 
Water to . ; 8 oz. 1,000 ccs, 
Caustic soda 40 grs. 18 g. 
Water to P 5 Oz. 1,000 ccs. 
Sodium hyposul- 

phite 1 OZ. 500 g. 
Water to . ; Paes 1,000 ccs, 


For use take of A 160 minims, B 240 minims,- 
C 20 minims, and water to make 1 oz. 


DEVELOPING MACHINE (Fr., Machine de 
développement; Getr., Entwicklungsma- 
schine) 

Various machines have been devised from: 
time to time for the semi-automatic develop- 
ment of plates or films, One of the most suc- 
cessful for films was introduced in 1903 by 
Kodak, Ltd., and may be worked in full daylight. 
The spool of film having been inserted in the 
machine and the lid closed, a handle is turned 
which winds the film face outwards against a- 
coiled ‘‘ apron ’”’ of celluloid, with ribbed rubber 
edges acting as separators between the layers 


——— 


Kodak Developing Machine 


of film. The developer is then introduced and. 
the film slowly rotated for a given time. It 
may next be washed and fixed in the same way 
and removed from the machine. Development 
takes from four to eight minutes, according to” 
the temperature. In a later pattern of the 
machine (see illustration), the film having been- 
wound into the red celluloid apron, is placed- 


Developing Tank 


in an upright cylindrical tank, and left for a 
Specified time in a dilute developer. A water- 
proof lid to the tank allows it to be reversed at 
intervals during development. 


DEVELOPING TANK (Fr., 
développement, Cuvette hermétique ; 
Enitwicklungsbehdlter) 

A metal or stoneware tank intended for stand 
or time development. ‘There are many different 
patterns for both plates and films. In the 
Watkins developing tank a metal rack, holding 
one dozen plates, is attached to the lid in such 
a way that when inserted in the tank the plates 
are horizontal; the advantage is that one or 
two plates only can be developed if desired, 
with but a small quantity of solution. The 
plates having been inserted in the dark-room, 
and the closely-fitting lid adjusted in position, 
the developer is poured in at a light-trapped 
delivery piece projecting at one end of the tank. 
This delivery piece serves not only for the 
admission and discharge of the various solutions, 
which inay be done in daylight, but can be used 
to hold a thermometer to give the temperature 
of the developer and the consequent time of 
development. Another typical developing tank 
is Griffin’s, in which the solutions are poured 
through a light-trapped funnel and run off by 
a tap at the side. A chain is attached to the 
tank by which it may be hung under a tap 
for washing the negatives after development. 

Tanks for “stand” development, in which 
the negatives are left for a long time in a dilute 
developer, consist usually of a grooved stone- 
ware trough with a lid; these require a dark- 
foom for the different Operations. (See also 
“Developing Machine.”) 


DEVELOPING TENT (Fr., Tente de développe- 
ment ; Ger., Entwicklungszelt) 

A portable folding tent for development out- 
doors, or in any place where no dark-room is 
available. In the wet-plate period every photo- 
gtapher was obliged to carry a dark-tent with 
him, as the plate had to be sensitised directly 
before use and developed immediately after 
£xposute. The few peripatetic ferrotype workers 
still remaining use a similar contrivance. Small 
‘portable developing or changing tents are often 
@ great convenience to travellers and tourists. 


DEVELOPMENT, CONFINED 

A system of development advocated in 1898 
by Colson, a Frenchman, but now rarely used. 
The principle was to restrict the amount of 
developer in contact with the plate. The 
Jatter was placed in the developer in the usual 
‘way; but suspended over it and nearly, if not 
quite, touching it was a sheet of plain glass ; 
or the exposed plate was soaked in water, and 
the plain glass in the developer, and the two 
placed in contact, repeating the process as often 
aS necessary. Colson claimed that less fog and 
clearer negatives were produced in this way. The 
‘process was recommended for over-exposed 
plates, the first of the methods above noted 
‘being employed. 


DEVELOPMENT, DAYLIGHT 
light Development.’’) 


Réservoiy de 
Ger., 


(See “ Day- 


174 


Development, Factorial 


DEVELOPMENT, FACTORIAL 

A system of determining the duration of 
development by noting the time of appearance 
of the first trace of an image on the plate and 
multiplying this time by a factor, the result 
being the total duration of development required 
to produce a negative of given density. This 
method was suggested by Alfred Watkins in 
1893, and has been found in practice to be very 
reliable except in a few cases of exceptionally 
low temperatures and yery dilute developers. 
It may be looked upon_as one of the first ptac- 
tical steps to reduce development from mere 
happy-go-lucky guesswork to a definite and 
exact method. Like all methods based on laws 
it is elastic and capable of adjustment to the 
individual worker’s ideas of what is a correct 
negative; or, in other words, by reducing or 
increasing the factor a thinner or denser nega- 
tive may be obtained suited to the particular 
printing process employed. It is an ingenious 
application of Hurter and Driffield’s law of con- 
stant density ratios, and is based on the fact 
that with correct exposure the total duration 
of development for a given density bears a fixed 
ratio to the time of appearance of the image, 
assuming that the developing power of the 
solution remains constant, and this rule holds 
good for variations in strength of the developing 
agent, in the amount of the alkali, bromide, and 
temperature. 

The following factors are those generally used 
for the principal developers :— 


Adurol * ‘: a 
Azol . ’ : * + Se 
Certinal : ; + 430 
Cristoid pyrocatechin . 30 
Diogen ; . F <) out 
Edinol ‘ : eae 
Hikonogen . ‘ " +e 
Glycine-potash ., 3 a 
Glycine-soda . So ay 


Hydroquinone + bromide ek 
Imogen sulphite . f + 
Kachin ‘ : 


Kodak powder . . shiRee 
Mequin ; ; ref 
Metol . ; ‘ : a DRS 
Metol-hydroquinone ., 14 
Ortol . : ; bi IO 
Paramidophenol . ; ae 
Pyrocatechin ‘ ; * 420 
Pyro-metol (Imperial Standard) 9 
Pyro-soda . . -4-15 
Quinomet . ; ; - 38 
Rodinal . : ; viene 
Synthol E : 30 
PYRO-SODA AND Pyro-PoTasH Factors 
Pyro Bromide Factor 
Grs. per oz. Grs. per oz. 
I 2 4 ; 9 
2 : 4 - 5 
3 . + . 43 
4 ; I : 4 
8 ‘ 2 ; 34 
I ‘ O ‘ 18 
2 ‘ fe) ‘ ves 12 
3 ie fe) ss 10 
4 oy ra) sts 8 
5 i fe) ve 64 


Development, Factors for 175 


Factors for soft, normal, and strong contrasts 
with “tabloid ’’ formule (Burroughs and Well- 
come) :— 

Soft Normal Strong 
Amidol . 4 ees IO 1s 
Edinol . pS 20 24 


Eikonogen : ae 12 15 
Glycine . , me crest 13 16 
Hydroquinone. oes 43 5 
Metol . ‘ pate”. 30 35 
Metol-hydroquinone. 10 14 16 
Paramidophenol ute 16 18 
Pyro : 4 ; 4 6 m 
Pyro-metol . ¥ 9 II 


The factor for a combined developer with the 
developing agents in equal quantities is the 
mean of the two, for example :— 


Pyro 6 Metol 30 
(6 + 30) + 2 = 18 


If the agents are not in equal proportions the 
factor for each is multiplied by the number of 
parts and the results added together and divided 
by the total number of parts of both agents; 
thus, supposing that the proportions were pyro 
4 parts and metol 2 parts, it would be— 


Ova ome 24 
et oy 2. a) OO 
60 + 24 = 84 +6 = 14, the factor 
required. 


The above factors are given merely as guides, 
and those that have been found to give a nega- 
tive of normal contrasts, that is, one with a 
= 1, but should the worker think that such 
a negative is too soft or too hard, he has merely 
to increase or decrease the factor to obtain 
greater or less contrasts. Supposing one were 
using a metol-hydroquinone developer with a 
factor of 15, and the time of appearance were 
9 seconds, the total duration of development 
would be 15 x 9 = 135 seconds. 

The great advantage of the factorial system 
is that it gives the beginner an excellent idea of 
how long to develop and enables even the 
advanced worker always to obtain negatives of 
similar character. 


DEVELOPMENT, FACTORS FOR 
“Development, Factorial.’’) 


DEVELOPMENT, FORCING 

When a plate is undet-exposed, many workers 
add more of the alkaline solution to the developer, 
and continue the development until the plate 
begins to fog, or until it is considered impossible 
to secure more detail. Although by this method 
of forcing development the utmost shadow 
detail is secured, it has the disadvantage of 
making the light tones much too strong and 
dense; and the result is a harsh negative, 
excepting in the case of subjects deficient in 
contrast, for which subjects this method is 
satisfactory. For all others, a better plan is 
to take the negative from the developer, let it 
test in plain water for about five minutes, and 
then continue development in a considerably 
diluted solution containing a large proportion 
of alkali. The dilute solution is thought to 
yield much softer contrasts, 


(See 


Development, Stand 


DEVELOPMENT PAPERS 

The opposite to print-out papers; they are 
papers on which the image is brought out by 
development after exposure. The principal and 
most widely used development papers are those 
known as bromide and gaslight papers, described 
fully under separate headings. Phosphate paper 
is also a development paper, and in some cases 
this is sold under fancy names. The above are 
development papers proper. Carbon is in a 
sense a development paper as the image cannot 
be seen until the exposed tissue has been washed 
in hot water. Platinum, ferro-prussiate, and 
the ferric papers are usually referred to as 
partial development papers, because the image 
shows very faintly after exposure, and needs 
development in order to bring it to its full 
strength. 

In the United States, the term ‘‘ development 
paper’ is applied exclusively to gaslight paper. 


DEVELOPMENT, STAND (Fr. Développement 
dans les cuvettes verticales ; Ger., Stand- 
entwickelung) 

This term was applied by Meydenbauer in 
1892 to a system of developing plates in upright 
grooved tanks in extremely dilute developers, 
though the system was first described by 
Wratten and Wainwright in 1882. Itis claimed 
for this process that the grain of the silver 
image is much finer than by any other method, 
that the gradations are truer and the results 
more uniform; in addition to which no visual 
examination is required, and therefore the plates 
are freer from fog. On the other hand, unless 
the developer be occasionally agitated there is 
considerable risk of peculiar local markings and 
stains. For many years after its reintroduction 
by Meydenbauer, extremely dilute solutions 
were recommended so that the duration of de- 
velopment was prolonged even up to twenty-four 
hours. Recently, however, a more sane view 
of the matter has been accepted, and time has 
been so considerably reduced that it has now 
practically been merged into “‘time develop- 
ment,’ (See “Development, Time.’’) 

It is often considered that the necessary in- 
crease in the duration of development is calcu- 
lable from the dilution—that is to say, if a 
normal developer takes three minutes to obtain 
a certain density, it will, when diluted ten times, 
require 3 x 10 = 30 minutes; this statement 
is not borne out by careful photometric measure- 
ments, and Wratten and Wainwright have 
published certain researches on the subject 
based on such measurements which disprove 
this assumption. They point out that stand 
development cannot be considered economical, 
as most of the commercial tanks require far 
too much developer; with 29 oz. for six half- 
plates, after half an hour’s development the 
solution is so oxidized as to be useless. The 
idea that a plate may be left in a stand developer 
for an indefinite time is also wrong; as is also 
the theory that a plate which should require only 
thirty minutes will be as much spoilt in an hour 
as the same plate developed for six minutes 
instead of three. It is as important, therefore, 
to know the correct duration of stand develop- 
ment as that of ordinary development. They 
further point out that the increase of time 


Development, Theory of 


required with rodinal is largely dependent 
upon the amount of air dissolved in the water 
to make the developer. For instance, a plate 
that required three minutes’ development with 
1:20 rodinal required forty-two minutes when 
developed with 1: 200 rodinal diluted with air- 
free distilled water, and not thirty minutes; 
forty-six minutes with ordinary distilled water, 
and fifty-two minutes with ordinary tap water. 
Pyro-soda and glycine are not dependent on the 
amount of air in the developer, but a ten times 
diluted pyro developer requires fifteen times 
the length of development with the strong 
developer. 

Edge markings are very liable to occur, due 
to the plates being too near to the edges and the 
bottom of the tank, and thus being starved of 
developer. Plates are also as liable to chemical 
fog in stand development as in any other kind, 
and therefore too prolonged development should 
be avoided or bromide should be added to the 
developer, in which case the exposure must be 
increased, and not the duration of development. 
Zinc tanks should be avoided, as they are very 
liable to be attacked by alkalis. 


DEVELOPMENT, THEORY OF 

The old theory of development was that the 
reducing agent or developer reduced the exposed 
silver bromide or latent image to metallic silver, 
and that the bromine combined with the alkali 
to form an alkaline bromide, and this is usually 
expressed by the following equation :— 


AgBr+ DNa = Ag+ NaBr+D 


in which D merely stands for the developing 
agent. This was satisfactory as far as it went, 
but it really explains very little. The later 
theories, which involve a consideration of the 
ionic theory, assume that when a salt is dis- 
solved in water it is split up into so-called ions, 
which are considered to be atoms of the elements 
carrying an electric charge. Metallic or basic 
ions are usually termed kations, and the acid ions 
are termed anions, the former carrying a positive 
and the latter a negative charge. Chemical 
reactions are now considered to take place 
between ions, and only when the substance goes 
into solution, and thus becomes dissociated 
otionised. According to this we might represent 
the formation of silver bromide by the following 
equation :— 


+ ~ + = + - + — 
K + Br+ Ag+ NO; = Ag Br+ K+ NO 


which roughly shows the dissociation of 
potassium bromide into the potassion K carrying 
a + ofr positive charge, and bromion carrying a 
— or negative charge, silver nitrate being dis- 


sociated into positive Ag + and negative 
nitrion NO; — then the final result would 
be :— 
+ — + - + = ier 
KBr + AgNO, =. AgBr + KNO, 


and as a positive and negative charge meet in 
AgBr this becomes unionised, and is precipi- 
tated as an insoluble precipitate. 

If now we apply this to development, and we 
assume the formation of an alkaline phenolate, 


176 


Development, Theory of 


as in the case of pyrogallol with only sufficient 
caustic soda to form this, we might represent the 
action as follows :— 


— + 
CONa 
HC COH ve a 
+ Ag + Br= 
HC COH 
HC 
CO 
HC COH + = 
Ag + + Na + Br 
HC COH 
HC 


That is to say, the pyrogallol loses a negative 
charge which neutralises the charge on the silver 
ion, No account is here taken of any change 
in the pyro, though such must take place, but 
the oxidation products are not well known. 

In the case of hydroquinone, however, where 
we know that the product formed from it in 
development is quinone, we can simply write 
the equation as follows :— 


COH Oc 
H CH CH CH 
e which is a no 
gi : : 
cH | CH ionised into CH CH 
COH CO 
hydroquinone ionjsed hydroquinone 
then 
OC (oe) 
CH CH ot CH CH 
+ 2Ag = 2 Ag + 
CH CH CH CH 
_ CO Ries : ee) 
pydscntnone + Oniehsiets ale 4 qbinone 


and the ionised hydroquinone has merely lost 
two negative charges which neutralise the 
positive charges of the silver in the ionised silver 
bromide, and the two oxygen ions combine to 
form quinone. ’ 

Obviously there are certain physical pheno- 
mena which one must take into consideration, 
and an emulsion consists of a number of particles 
of silver bromide embedded in a jelly. The 
modern theory of a jelly is that it consists of a 
number of minute cells with passages in between 
ramifying in all directions, and the cells and. 
passages contain a weak solution of gelatine, 
whilst the cell walls are formed of a very strong 
solution. In each cell we may imagine a grain 
or particle of silver bromide, and for the developer 
to reach this it is obvious that it must first 


Development, Theory of 


traverse the passages, and then diffuse through 
the cell walls. The first is termed macro-diffusion, 
which takes place at a rapid rate, and the later 
action, which is comparatively slow, is known as 
micro-diffusion. It has already been pointed 
out that a chemical reaction can only occur when 
the silver bromide goes into solution and is 
ionised into + Ag and — Br. The instant 
the developer reaches the dissolved silver it is 
reduced to the metallic state and deposited, 
provided there be some nucleus or germ on which 
it can deposit. This nucleus is the latent image 
(which see). Were there no nucleus, then the 
silver would accumulate in solution till super- 
saturation occurred, and then the chemical 
action would cease. As soon as the dissolved 
silver is deposited, fresh silver takes its place, 
and so the process proceeds till the whole of 
the silver available is reduced. 

In the above rough sketch of what is supposed 
to take place, we must not lose sight of the 
important fact that, as pointed out in the note 
on the latent image (which see), Scheffer has 
proved that the action of light is to cause 
the protrusion of filaments or threads from the 
sensitive salt grain, and therefore these would 
rupture the cell walls, and so render the access 
of the developing agent much easier. 

Now, if we consider what happens when a plate 
is developed, we shall at once see that at first 
we shall have some silver halide grains, which 
are so affected by light as to be readily reduced 
by the developer, and some which are not affected. 
As development proceeds we shall have (a) 
some grains already reduced to metallic silver, 
(b) others not yet completely reduced, and (c) 
others which are not light-affected and there- 
fore not attackable by the developer. Natur- 
ally, at first the progress of development will be 
rapid, as the whole of the light-affected grains 
will be capable of development, but as it pro- 
ceeds there will be fewer and fewer of the (b) 
grains, so that development gradually gets 
slower and slower, and we may express this 
by saying that: the rate of increase of density 
= constant (maximum density attainable — 
density obtained). 

Here the constant or velocity constant is 
usually termed K. 

If the temperature of the developer be raised 
then the velocity constant, or K, increases, and 
this is termed the temperature coefficient, which 
is generally defined as the ratio for correct 
development at 10° C. (50° F.) difference of 
temperature. 

The efficiency of a developer E is the velocity 
of development compared with ferrous oxalate 
at 20° C., divided by R, which is the reducing 
power, or the number of grain-molecules of 
AgBr reduced by one grain-molecule of the 
developing agent. The energy F is the con- 
centration of bromide producing the same 
retardation of development as with ferrous 
oxalate for o-o1” potassium bromide. For 
a complete mathematical treatment of the 
subject, the reader is referred to “Theory of 
the Photographic Process,” by Sheppard and 
Mees. 

Before leaving this subject it would be as well 
to consider the question of the chemical constitu- 
tion of the actual developers or reducing agents. 

12 


177 


Development, Theory of 


Of late years the number of developers has been 
largely increased, and a glance at their true 
chemical names will at once prove that they are 
highly complex organic substances belonging 
to the benzole or naphthalene series, 

Benzene or benzole has the formula C,H,, but 
in 1865 Kekulé, from a long series of experiments, 
came to the conclusion that the six atoms of 
carbon in benzene form a closed-chain or nucleus, 
and that the molecule of benzene is symmetrical, 
and that each carbon atom is directly united 
with one, and only one, atom of hydrogen. The 
graphic formula usually adopted is as follows:— 


H 
é 
H—C C—H 
H—cC C—H 
Cc 
i 


Now, in the above formula it is obvious that 
if two of the six hydrogen atoms were replaced 
by two other atoms or groups they might be 
arranged in one of five different ways, as shown 
in the accompanying diagrams, in which, for 
the sake of clearness, the C atoms are omitted 
and the added group or atom expressed by +.. 


# x * x x 
| | | | [ 
—x 4— 
=a a4— 
| 
x 


I II III IV Vv 


Then, if one x group occupies any given position, 
that numbered 1, for instance, the other may 
occupy 2, 3, 4, 5,or 6. But these five formule 
only represent three isomeric compounds, that. 
is, compounds of the same composition C,H,7%. 
and not five, because it is obvious that IV. and 
V. are practically identical with I. and I., which. 
may be at once seen by writing them on thin paper 
and looking at them first in the normal way and 
then through the paper. In order to distinguish 
these three compounds, they are said to be in the: 
ortho, meta, and para positions :— 


x x % 
x 
* 
x 
Meta 


Ortho Para 


Now, obviously in the ortho position the two 
*% groups are joined to carbon atoms which are 
directly united or are next to one another, so 


Development, Theory of 


that we could actually represent an ortho 
compound as 


x | x 
I I 
fT Aa x x 
or or or or or 
Le 5 Bix x x 
4/* \4 
x x 


r-2 ortho 2-3 ortho 3-4 ortho 4-5,ortho 5-6o0rtho 6-1 ortho 


Exactly in the same way, the meta compounds 
could be represented by placing » x at 1—3, 
2—4, 3—5, 4—06, 5—1 and the para at 1—4, 
2—5, or 3—6 positions. 

Now, it has been proved by Lumiére and 
Seyewetz and by Andresen that a developer must 
have two hydroxyl OH groups or two amido 
NH, groups joined to the benzole ring, and 
that these groups must be either in the ortho 
or para positions to be developers, The latter 
compounds are the stronger developers, the 
ortho compounds the weaker, whilst the meta 
compounds are not developers at all. If one of 
the hydrogen atoms of a hydroxyl group be 
replaced by an alkyl radicle—that is, an alcohol 
tadicle, such as ethyl C,H,—or by another 
radicle, then the developing power is destroyed, 
as, for instance, in phenetroin 


CC,H, 


NH, 


If, on the other hand, one of the hydrogen atoms 
of an amido group be replaced by an alkyl 
radicle, then the developing power is increased, 
as in the case of 


OH OH 
and 


NH, 


Para-amidophenol 


NH CH, 
Monomethyl - para- 
amidophenol or metol 


Besides the OH and NH, groups, the hydrogen 
atoms of the benzole ring may be replaced by 
other radicles, such as carboxyl COOH, and 
the sulpho group SO;H, but these reduce the 
developing power, and in this case the position 
of the added or substituted radicle plays an 
important part, as in the instance of 


OH OH 


CO,.H 
and 
CO,H 


NH, 
Para-amidopheno|— 
ortho-carbonic acid 


2 
Para-amidophenol— 
meéta-carbonic acid 


the former being but a very weak developer, 
whilst the latter is a vigorous one. 
If a hydrogen atom be replaced by one of the 


178 Development, Theory of 


halide atoms Cl or Br, then the developing power 
is increased, as in the case of 


OH OH 
6 (). or Br 
OH OF 


Para-dihydroxybenzole 


Monobrom or monochlor-para- 
or hydroquinone 


dihydroxybenzole or adurol 


If three hydrogen atoms in the benzole ring 
are replaced by three NH, or OH groups, then 
the developing power is increased, and here, 
as in the case of the di-substitution products, 
the ortho-, meta-, or para position plays an 
important part, thus 


OH OH 
OH OH 
is weaker than 
OH 
Ortho-dihydroxybenzole Ortho-trihydroxybenzole 


or pyrocatechin or pyrogallol 


because in the former there are only two OH 
groups in the ortho position, whilst in the latter 
there are three OH groups all in the ortho 
position. Again, if one OH and one NH, group 
be added to the ring, then we have a still more 
energetic developer, as in the case of 


OH 


para-amidophenol, the 
base of rodinal; 


NH, 
whilst the addition of another NH, group in- 
creases the action still further, as in the case of 
OH 


NH, 
1-2-4 diamidophenol 
or amidol, 


NH, 


which is at once an ortho- and a para-amido- 
phenol, and diamidoresorcin 


OH 


NH, 
1-—3-4—6 diamidoresorcin 
H 


NH, 


a double para-amidophenol, in which the OH 
and NH, groups, as shown by the Hines, are in 
two para positions; this is still more energetic. 

There are two developing agents which belong 
to the naphthalene Cj») H, series, and naphthalene 
may be considered as two benzene rings joined 
together, and which at the points of junction 


Development, Thermo 


have lost their hydrogen atoms, so that we may 
write naphthalene graphically as 


Cc 
CH CH 
Here, too, the hydrogen atoms may be replaced 
by other atoms or groups, and we have 


NH, 
OH a, amido-, 8, naph- 
thol-, 8, sulphonic acid 
50;H or eikonogen, 
and 
NH, 
OH a, amido-, 8, naph- 
thol-, 8B, Bs acid sul- 
S0,Na SO,H phonate of soda or 


diogen. 


It will be easily seen that the Greek letters 
and the numbers refer to the positions of linking 
of the substituted atoms. In the above sketch 
the developing bases only have been considered, 
for many of the actual developers are salts, such 
as chlorides, sulphates, oxalates, etc., of these 
bases. 


DEVELOPMENT, THERMO 

A name invented by Alfred Watkins for a 
system of developing in which the duration of 
development is varied as the temperature of the 
developer varies, to distinguish it from “ time 
development’”’ pure and simple. Although it 
had been known for a long time that develop- 
ment was prolonged in cold solutions, Houdaille 
in 1903 was one of the first to suggest a definite 
rule, in conjunction with hydroquinone, to the 
effect that a variation in temperature of the 
developing solutions of 1° C. caused a variation 
of 5 per cent. in the time of appearance of the 
image and the duration of development. In 
1905 Ferguson and Howard published a method 
of obtaining a given gamma or degree of contrast 
with a developer of constant composition at 
varying temperatures by developing strips of a 
plate exposed behind a sector wheel for different 
times, measuring the gammas obtained and plot- 
ting them on a chart. Later, Ferguson sug- 
gested a simpler method, in which only two strips 
were developed for given times and the tempera- 
ture coefficient of the developer found by a very 
simple logarithmic calculation. The objection 
to both these methods is that a sector wheel 
and photometer are required. As, however, 
Ferguson’s method is simple, and the basis of 
that to be described later, it is briefly given here. 

The first thing to determine is what is known 
as the temperature coefficient of the developer 
used, or the increase in velocity of development 
for a rise of 10° in temperature, from which the 
increase in rapidity of development for 1° can 
be found by dividing the logarithm of the 
temperature coefficient by 10.. The usual 


179 


Development, Thermo 


mathematical expression for 
coefficient is— 

velocity at (¢ + 10°) C. _ p10. 
velocity at 7° C, Py! ‘ 


therefore b, or the increase for 1°, is— 


the temperature 


log. of temperature coefficient 
10 


Ferguson has suggested that two strips of a 
plate should be exposed to the same graduated 
series of light and one developed at ¢° C. and the 
other at 7° + #° C.; then the times required 
to obtain the same gamma or degree of contrast 
on each plate will be M and m, and as the times 
are inversely proportional to the velocities 


log. M — log. m 
% 


in which 6 = the temperature coefficient for 1°C., 
and 10 log. 6 will be the temperature coefficient 
for 10° C. 

To make this quite clear two strips of a plate 
should be developed so as to show the same 
degree of contrast, one at a given temperature 
and the other at this temperature plus a certain 
number of degrees. Two strips A and B of a 
plate were exposed to the same graded series of 
light, and A took 3$ minutes to obtain a gamma 
= 1 at 10° C. and B took 24 minutes at 18° C., 
then— 


es log. b, 


log. b = 


log. 3°5 = *544I 
log. 2°5 = +3979 
"1462 


Now the difference of temperature (A as it is 
usually written) was 18 — 10 = 8° 
oh. ft 462 se Byes s0082.= log. b 

.°. 10 log.b = ‘0182 x 10 = °182 = the tempert- 
ature coefficient for the plate and developer used. 
Having found the above, to find the necessary 
duration of development at 14° C. to obtain the 
same gamma the formula is— 


log. M — x log. b = log. m 


or, in words, from the logarithm of the time 
required at 10° C. subtract 14 — Io = 4 times 
log. b, and the result will be the logarithm of 
the time required ; assuming that log. b = -0182 
as above, then— 


log. 3°55 = *544I1 

4 log. b= -0182 x 4 = :0728 

"4713 = log. of 2-96 
minutes, the time required. 

Watkins has done away with the sector wheel 
or graded series of lights and the finding of 
the gammas; he merely exposes a plate on a 
landscape including some sky and cuts it in 
two, or makes two exposures. It is essential to 
have some means for warming up the developer, 
dish, and measure, and also to have a thermome- 
ter. When the developer, dish and measure are 
warmed up, say to 75° F. (about 24° C.) the 
plate is placed in the dish and flooded with the 
developer, the time accurately noted, and the 
first appearance of any image also noted; the 
plate being now of no further use it may be 
thrown away. The second half of the plate is 
now developed in a developer of exactly similar 
composition, only colder, the time of appearance 


Development, Time 


noted, and we have all the factors necessary for 
finding the time of development for any tempera- 
ture with that particular plate and developer 
if we know also the factorial number (see ‘‘ Devel- 
opment, Factorial’’) of that developer. Sup- 
pose, for example, that a metol-hydroquinone 
developer with a factor of 15 is being used, 
and it is found that at 50° F. (10° C.) the first 
appearance of the image takes place in 4o 
seconds and at 66° F. (18-8° C.), the first appear- 
ance takes place in 28 seconds; then turning 
to a table of logarithms we find that log. 4o = 
1'602060 and log. 28 = 1°447158, then— 


1°602060 — 1°447158 = 0*154902. 


Now the difference in temperature is 66 — 50 
= 16, then 0-154902 + 16 = -009681 = log. of 
28-3 seconds, and as the factor for this developer 
was 16, then. 28-3 .x 15° = 424 ‘seconds, = 
7 minutes practically, which is the time required 
to develop the plate at 57° F. (14° C.). 

It is obvious from this that we can calculate 
a table for every degree (or two degrees will be 
enough) rise or fall in temperature of the 
developer, by multiplying the log. factor by 2 
and adding for every two degrees drop or sub- 
tracting in the case of a rise, and then multiply- 
ing the number by the factorial number. This 
may seem somewhat complicated, but the 
logarithms have merely to be read from a mathe- 
matical table-book and simple division, multi- 
plication, and subtraction performed. 


DEVELOPMENT, TIME 

Practically, this method of development was 
established upon a sound basis by the researches 
of Hurter and Driffield, who proved that it was 
only necessary to reduce or increase the duration 
or time of development in order to obtain nega- 
tives of any desired degree of contrast, and that 
it was not necessary to tinker with the con- 
stituents of the developer. The outcome of this 
work was the slow recognition of the fact that 
it was advisable to use a given developer at a 
given temperature for a given time to obtain 
a particular class of negative. This method is 
particularly valuable in the case of colour- 
sensitive plates, which may be immersed in the 
developer completely protected from light, and 
at the end of the stated time washed and fixed. 
(See also “‘ Development, Thermo.’’) 


DEVIATION (Fr., Déviation ; Ger., Abweichung) 

An optical term denoting the alteration in the 
course of a ray of light when bent from its 
original path by refraction or reflection. The 
length of a prismatic spectrum alters according 


> 
mek 
ad 
- 


- 
me 
~ 
= 
-~ 


ma. 


Deviation of Rays Passing Through Prism 


to the position of the prism with reference to the 
trays of white light falling upon it (“incident 
rays’’). When the prism is so placed that the 
spectrum is practically at its shortest length, 


180 


Dialyser 


which happens when the mean emerging tays 
(say the green, at the # Fraunhofer line) and the 
incident rays make the same angle with the 
ptism, as shown in the illustration, the latter 
is said to be in the position of “ minimum 
deviation.” 


DEXTRINE (Fr., Dextrine; Ger., Dextrin) 

Known also as British gum. This white or 
yellowish-white powder, soluble in water, in 
which it forms a viscous and gummy solution, 
insoluble in alcohol and ether, has the formula 
(C,H,,0;)x. The pure substance is made by 
submitting starch paste to the action of malt 
extract; after filtering, maltose is precipitated 
by repeated treatment with alcohol, and finally 
the dextrine is thrown out by adding sufficient 
absolute alcohol. It is also made by the action 
of heat or of nitric acid on potato starch. It 
has the same chemical composition as starch, 
but its properties are different. The principal 
use of dextrine isin the making of mountants 
(which see). There is a further variety, of a 
brown colour, but this is not used as a mountant, 

Iu process work, dextrine has been advocated 
as an addition to the etching bath, the addition 
of gummy matter to the bath being claimed to 
facilitate etching and keep the etched surface 
bright. Dr. Albert has recommended a powder, 
which is believed to be a mixture of dextrine and 
powdered alum, for use with the nitric acid 
solution, to cause a frothing of the bath; the 
theory is that the solution is oxygenated and the 
hydrogen gas given off is absorbed. 


DEXTROSE 

Known also as glucose and grape sugar ; a white 
crystalline solid, formula C,H,,O,, readily soluble 
in water. It has been recommended as an 
addition to mountants and as a preservative 
for plates, but is now rarely used. Itis employed 
in some processes of silvering glass. 


DIACTINIC (Fr., Actinique; Ger., Aktinisch) 
Capable of passing actinic or photographically 
active light; the opposite of non-actinic. 


DIAGONALS OF PLATES (See “ Sizes.’’) 


DIAGRAMS AS LANTERN SLIDES. (See 
‘“‘Qantern Slides, Diagrammatic.’’) 


DIALYSER 
A parchment, skin, or paper stretched over 
the open end of a glass or wooden vessel, which 


Dialyser 


is then placed in an outer container of water 
(see illustration). Into the dialyser are poured 
liquids such as thin solutions of gelatine or 
other colloid containing salts, the latter diffusing. 


Diamidophenol 181 


through the septum into the water, and leaving 
the gelatine or other colloid in the dialyser. In 
the illustration, a is the dialyser, B the outer 
vessel of water, and c the septum or skin. 


DIAMIDOPHENOL (See ‘“‘ Amidol.’’) 


DIAMIDOPHENOL HYDROCHLORIDE (See 
“ Amidol.”) 


DIAMIDORESORCIN (Fr. and Ger., Diamido- 
vesoryctin) 

C,H, OH OH NH, HCI NH, HCl. Molecular 
weight, 153. Solubilities, soluble in water, more 
soluble in sodium sulphite solution. It is a com- 
plex organic salt, very similar in its action to 
amidol, and, like that, developing in the presence 
of sodium sulphite only. (See also “ Diamine.”’) 


DIAMINE 
A form of diamidoresorcin (which see) intro- 
duced by Lumiére as a developer. A formula is :— 


Sodium sulphite (anhy- 


drous) . 250 grs 30 g 
Diamidoresorcin Rakes os Ae get 
Water to “ Soy eGy OZ 1,000 ccs. 


DIAMOND LENS 

In the early days of photographic optics 
experiments were made with every kind of 
transparent body which could be formed into a 
lens. Claudet had a small lens fashioned from a 
diamond, expecting much from the high refrac- 
tion of this substance. However, it was not 
found to be of any practical value. It was 
destroyed in a fire at Claudet’s Regent Street 
studio, London. 


DIANOL 

Lumiére’s preparation of oxalate of diamido- 
phenol or amidol (which see), which is claimed 
to be rather more soluble than the hydrochloride, 
the usual salt employed. 


DIAPHAN, AND DIAPHANOTYPE 

An obsolete process used for obtaining trans- 
parent pictures for viewing in a diaphanoscope. 
Diaphan pictures were upon paper, and diaphano- 
types upon glass, but the terms were often 
reversed, and in the end all the pictures were 
known as diaphanotypes. The process as 
advocated by Thomas Sutton (published Decem- 
ber 15, 1856) was as follows: ‘‘ Thin photo- 
graphic paper must be employed. Immerse for 
half an hour in a solution of 20 grs. ammonium 
chloride; hang up and dry. Sensitise by float- 
ing on a bath of nitrate of silver, containing 
50 grs. of nitrate to 1 oz. of water; hang up in 
the dark to dry. In printing, apply the back 
of the paper to the negative and print through 
the paper very deeply. In this way the silver 
in the heart of the paper becomes reduced. 
Wash well, and tone in a weak gold bath made 
by adding 15 grs. of gold chloride in 20 oz. of 
water to a solution of 50 grs. of hyposulphite 
of soda in another pint of water. Leave the 
print immersed till it is thoroughly toned, then 
fix it in one part hypo to ten parts of water. 
The hypo reddens it slightly, but it becomes 
perfectly black on drying. Wash as usual, dry, 
and wax.” Sutton also advocated a develop- 


Diaphragms 


ment process for producing the pictures. Other 
workers made an ordinary paper print trans- 
parent with wax or Canada balsam, backing it 
up with a duplicate print, while others coloured 
their pictures. At the end of the diaphanotype 
“craze,” the pictures resembled crystoleum 
pictures, 

The terms were also applied at one time to 
lantern slides and window transparencies, both 
plain and coloured. 


DIAPHANOSCOPE _ (Fr., 
Ger., Diaphanoskop) 

A contrivance, much resembling the aletho- 
scope, pantoscope, or lanternoscope, intended 
for the exhibition of transparent positive photo- 
graphs. It consists of an enclosed box, which 
may or may not be furnished with a lens, the 
pictures being placed inside at a distance from 
the eye preferably equal to the focal length of 
the lens with which the negative was obtained. 


DIAPHRAGM SHUTTER (Fr., Obturaieur 2 
diaphragme ; Ger., Blende-verschluss) 

A shutter made to work between the two com- 
binations of a compound lens—that is, against 
the ciaphragm, and opening from and closing 
to the ccutre. It is obvious that the shutter 
itself acts as an expanding and contracting 
diaphragm, though not necessarily circular, and 
that consequently a large part of the exposure 
is practically given with a smaller aperture than 
that of the fixed diaphragm. The definition of 
the lens is thus improved, but the efficiency of 
the shutter (the relative proportion of the expo- 
sure during which it is fully open) is rather low. 
When of good quality, diaphragm shutters give 
excellent results. They are much used on the 
better-class hand cameras, and are usually so 
fitted as to form part of the lens mount. The 
exposures marked on cheap diaphragm shutters 
are seldom reliable. 


Diaphanoscope ; 


DIAPHRAGMS (Fr., Diapbhragmes ; Ger., Blen- 
den) 

A diaphragm is the aperture, fixed or remov- 
able, used in front of a single lens and between 
the combinations of a double lens, generally 
referred to as the “stop.”’ The various forms 
of diaphragms, systems of marking, values, etc., 
are as follow :— 

Various Forms.—tThe three patterns in general 
use are known as “rotating,” “‘ Waterhouse,” 
and ‘“‘iris.’’ Very cheap lenses, and those of 
obsolete patterns, are usually fitted with fixed 
stops, or pierced circles of metal which are let 
into the lens tube. Rotating stops are mostly 
fitted to wide-angle and landscape (single) lenses, 
and are employed in many hand cameras; a 
series of circular holes of various sizes are 
pierced round the margin of a revolving disc 
fitted to the lens mount. Waterhouse dia- 
phragms were invented by John Waterhouse, 
of Halifax, in 1858, a circular aperture being 
cut in a thin piece of sheet metal and inserted 
into a slot in the lens mount, a separate piece— 
called a stop—being required for each opening. 
The “‘iris,’’ the most modern form of diaphragm, 
consists of a series of curved plates of metal, 
vulcanite, or other material, fitted inside the 
lens tube and attached to a ring on the outside 


Diaphragms 


of the lens mount; by revolving the ring the 

lates are made to open and close, thus form- 
ing apertures of various sizes. Some Continental 
lenses have other forms of stops, but they are 
rapidly falling into disuse. The form in which 
the diaphragm is made does not affect its action 
on the lens in the least, and optically one stop 
is as good as another; it is in the matter of 
convenience where one pattern has any advan- 
tage over another. The iris pattern—so named, 
by the way, because it opens and closes like the 
iris of the eye—is undoubtedly the most con- 
venient and popular pattern. 

Systems of Marking.—There are at least half a 
dozen systems of marking. Stops are marked 
with numbers, such numbers, as a rule, appear- 
ing upon the iris ring or lens mount when the 
iris system is used, upon the top or handle of a 
Waterhouse diaphragm, and upon the circular 
revolving disc in the case of rotating diaphragms ; 
in the last-mentioned case the number appears 
opposite to the aperture which it indicates, so 
that when the stop is in use in the lens itself its 
number is visible outside the lens tubes. In- 
cluded in the stop-marking systems in vogue 
‘are the “f,’’ “U.S.,’”’ ** Dallmeyer,” ‘* Goerz,” 
“‘ Zeiss,’ and “ Voigtlander,’ besides many 
others. The “f” and “U.S.” systems are 
adopted for all but 1 per cent. of the lenses in 
general use, and of these the former is the more 
popular, especially in England, it being in 
a sense self-explanatory. The ‘“f’’ number 
simply means the proportion of the diameter 
of the stop to the focal length of the lens. For 
example, f/8 is of a diameter one-eighth the 
““focus’’ of the lens. The “f” value of an 
unnumbered stop cam be ascertained by dividing 
the focal length of the lens by the diameter of 
the stop. For example, a I-in. stop with a lens 
of 8-in. focal length is known as f//8; a $-in. 
stop with the same lens, f/16; a 4-in. stop with 
the same lens, f/32, and soon. Thus the “f”’ 
number is not a fixed dimension, but always a 
relative one, varying with the lens employed ; 
obviously f/8 with a 16-in. lens would mean a 
diameter of 2 in., whereas with an 8-in. lens it 
would mean a diameter of 1 in. Strictly, the 
“f’? numbers should be 4, +7, 74, etc., but the 
fractional form is ignored, and the numbers 
spoken of as 8, 11, 16, etc. Stops of definite 
“f’? values may easily be cut to the required 
size. Suppose, for example, that with a lens of 
6-in. focal length, an f/16 stop is required, 
then, 6 divided by 16 = 8, = 3; thereforé, 
the stop must be # in. in diameter, 

While, in the above rough-and-ready system 
of measuring, the ‘‘f’”’ value of a stop may be 
accurate enough in the cases of ordinary rapid 
rectilinear and single lenses, extreme accuracy 
is essential in the case of modern and improved 
anastigmat lenses ; for while a slight error may 
be of little moment with a small stop, the same 
amount of error—which error is, of course, 
proportional to the aperture—becomes serious 
with large stops, which are a feature of anas- 
tigmat lenses. It is necessary in such cases 
to consider the effective aperture. The stops on 
a modern lens by a good maker are always 
correctly numbered, and it is only when a worker 
attempts to check the optician’s calculations by 
dividing the focal length by the aperture that 


182 


Diaphragms 


he finds an imaginary error. The division 
system described above leads to false conchu- 
sions when some modern anastigmat lenses are 
measured by it, because of the great condensing 
power of the lens in front of the stop, from which 
lens measurements are taken. To quote an 
example; one of the most expensive of anastigmat 
lenses has a stop the value of, and marked, f/8; 
but the aperture of the stop is one-ninth the focal 
length, and, according to the rough and ready 
rule given above, would be f/9; while the stop 
marked f/5, although accurate, is f/7 according 
to the division method. ‘The following method 
of finding the effective aperture of a stop is more 
reliable with all kinds of lenses. The camera is 
set at “infinity,” or a distant object is focused 
upon the ground glass. A piece of card is then 
put in the place of the ground glass, or pasted 
thereon, so as to entirely cover it. In the 
centre of the card, and on the spot exactly 
opposite the lens, is made a hole the size of a 
pin’s head. The camera is then taken into the 
dark-room, and by the assistance of a ruby or 
orange light a disc of bromide paper is cut to 


- fit the inside of the lens cap. The cap, with the 


sensitive paper inside it, is then placed on the 
lens in the usual way, the sensitive side towards 
the stop. A lighted candle is then held against 
the hole in the cardboard for about half a 
minute, so that the light may travel through 
the camera, lens and stop to the bromide paper. 
The latter, after exposure, is taken out and 
developed, when a circular black spot will 
be found thereon, and the diameter of this 
spot will be the effective diameter of the stop 
used. If the exposure is made with the largest 
stop, the developed spot gives the effective 
aperture at which the lens will work, and the 
focal length of the lens divided by this, the true 
aperture, gives the “‘f”’ number. 

Opticians have adopted standard “‘f’’ numbers, 
namely, 3°16, 5:66, 8, 11°3, 16, 22°6, 32, 45, and 
64, but stops may be “in between” any of 
those named, or larger or smaller than 3°16 and 
64 respectively. As a general rule, 11-3 is 
spoken of as 11 and 22°6 as 22, but in the case 
of larger stops the decimal point, when it occurs, 
is always mentioned, as, for example, 4:5, 5°8, 
6°8, etc. 

The “U.S.”’ system (now practically obsolete 
in England) has long been popular in the United 
States, for which reason the initials are looked 
upon as indicating that country. Such, how- 
ever, is not the case. “U.S.” stands for 
“uniform system,” as an attempt was made, 
first of all in 1881, by the Royal Photographic 
Society to induce all lens makers to adopt a 
uniform system of marking diaphragms. 

The Royal Photographic Society’s standards 
and recommendations (dated tI901) are as 
follow :—(1) That intensity ratio be defined as 
dependent upon the effective aperture (and not 
upon the diameter of the diaphragm) in relation 
to the focal length of the lens. (2) That effec- 
tive aperture be determined in the following 
manner: The lens shall be focused for parallel 
tays; an opaque screen shall be placed in the 
principal focal plane, the screen being provided 
in its centre (in the axis of the lens) with a 
pinhole; an illuminant shall be placed imme- 
diately behind the pinhole and the diameter of 


Diaphragms 183 


the beam of light emerging from the front sur- 
face of the lens shall be the measure of the 
effective aperture. Note.—It will be found, 
except when the diaphragm is situated in front 
of the lens, that the diameter of the diaphragm 
itself is seldom identical with the effective 
aperture. (3) That every diaphragm be marked 
with its true intensity ratio, as above defined, 
in the following order of sequence: //4, 
f/s°6, f/8, f/113, f/16, f/22-6, f/32, f/45°2, 
f/64, etc., each diaphragm requiring double 
the exposure required by the preceding dia- 
-phragm. Should the greatest effective aperture 
of a lens not conform exactly to one of the 
intensities set forth above, this aperture should 
be marked in accordance with the definition of 
effective aperture, but all succeeding smaller 
apertures should be marked in uniformity with 
the above sequence. 

Stops marked by the Uniform System are 
commonly known as Nos. 1, 2, 4, 8, 16, 32, 64, 
128, and 256; the respective ‘“‘f’ values are 
Bee ee PAO. 22, 42, AS, and 64. 

Most of the lenses produced in France are 
marked according to the method advocated by 
the Paris Congress of 1889. /f/1o0 is taken as 
the unit aperture, the series advancing as the 
** Uniform ”’ system ; No. 1 is f/10, No. 2 f/14, 
No. 4 f/20, and so on. 

Influence of Diaphragms on “‘ Rapidity.’’—The 
“‘rapidity”’ of a lens depends upon the stop 
used. The “U.S.” numbers indicate relative 
exposures, but the “f’’ numbers do not, although 
the relative exposures are easily calculated from 
them. To find out the relative values of the 
““f” stops, first square them, and the exposure is 
then as one product is to the other. Thus, 
f/16, for example, requires four times the 
exposure necessary with f/8, because 16 x 16 
= 256, which is four times 8 + 8 = 64. When 
makers mark their stops as follows, f/8, 11, 16, 
22, 32, 45, and 64, each stop requires double 
the exposure of the preceding one and half that 
of the succeeding one. 

The Use of Diaphragms.—The main functions 
performed by stops are as follow :—(1) They 
govern the definition. A large stop, such as that 
generally used for focusing, may produce an 
indistinct image upon the focusing screen or 
sensitive plate, and it may be necessary to insert 
smaller stops into the lens in order to secure 
better definition. If, say, an object a few feet 
from the camera is sharply focused with a large 
stop, the background and surroundings may not 
appear sharply defined. The insertion of a 
smaller stop serves to cut down the area of the 
base of the cone of light formed by the lens, 
and the result is increased definition (see “‘ Depth 
of Definition’’). (2) To correct functional errors 
(as covering power)in a lens. Lenses not of the 
modern and improved anastigmat pattern have 
certain optical errors which show themselves 
when very large stops are used, and many of 
the older and even modern common lenses do 
not yield a sharp image all over the plate, 
a defect that is corrected by the use of a small 
stop and consequent increase in exposure. (3) 
To add to, or subtract from, the number of 
planes in a picture. All views are composed of 
various planes, or distances. When a large stop 
ia used, only one plane is in focus, and the 


Diazotype . 


smaller the stop the greater the number of planes 
made clear and sharp. 

In process work, various forms of diaphragm 
apertures are used, with the object of promoting 
the dot formation. The principle is that the 
apertures in the ruled screen act as pinhole 
lenses and form an image of the diaphragm, so 
that in this way the shape of the dot image is 
controlled. The square diaphragm is most 


B. Adjustable 
Diaphragm 


A. Penrose Diaphragm 
System 


commonly used, but squares with extended 
corners are also employed to promote the 
joining up of the dots in the high lights. 
The Penrose diaphragm system A standardises 
the use of such stops, the apertures being 
arranged on the basis that each smaller stop 
requires an exposure of half as much again 
compared with the next larger size. The 
adjustable diaphragm B enables any size of 
Square opening to be formed. 


DIAPOSITIVE 

An old name for a lantern slide or similar 
transparency made to be viewed by transmitted 
light. The name differentiated transparencies 
from positives upon opaque supports as, for 
example, daguerreotypes, ferrotypes, and wet 
collodion pictures backed up with black material. 


DIATOMS, PHOTOGRAPHING (See 
‘* Photomicrography.’’) 


DIAZOTYPE 

There are several printing processes based 
on the light-sensitiveness of the diazo compounds, 
which, although not much used, are of con- 
siderable interest, as they give a great range of 
colours. The diazo compounds are extremely 
tich in oxygen, and are formed by the action 
of nitrous acid on the aromatic amines, amido- 
sulphonic acids, amidocarbonic acids, etc., and 
readily combine with certain phenols and 
amines to form azo dyes. If a paper or material 
impregnated with a diazo compound is exposed 
under a negative, the diazo compound is decom- 
posed by the action of light, and on immersion 
in a solution which forms a dye with the diazo 
compound a negative image is obtained. 

The primuline process invented by Green, 
Cross and Bevan in 1890 is based on the light- 
sensitiveness of the diazo compound of primuline, 
a yellow water-soluble dye which dyes material 
or paper without a mordant. Paper or material 
is immersed in a solution of :— 


Primuline F - 320 grs, 
Hot water to . of -20n0R, 


33 &- 
1,000 ccs. 


Diazotype 184 


and then washed and immersed in— 


Sodium nitrite . 64 gts. 6°6 g. 
Hydrochloric acid . 150 mins. 15 ccs. 
Water to. : 20 OZ. 1,000*. 5, 


It should then be dried in the dark and exposed 
under a vigorous positive till those parts under 
the bare glass are colourless. Then wash 
thoroughly with water, and treat with one of 
the following solutions :— 


For Red 
8-Naphthol ; - 9°6 gts. Io g. 
Sodium hydrate me RPO, ree 2 Ra 
Water to. : 20 OZ. 1,000 ccs, 
For Orange 
Resorcin . : . 64 gts. 6°6 g. 
Sodium hydrate , EO ae Oa 
Water to. 20 OZ. 1,000 ccs. 
For Purple 
a-Naphthylamine . 190 grs. 20 g. 
Hydrochloric acid I OZ. 50 ccs. 
Water to. : Way? * ata 1,000. ,; 
For Black 
Eikonogen ». 12%, gre. 13 g. 
Water to. 20 OZ. 1,000 ccs. 
For Brown 
Pyrogallol . I13 grs. I2 g. 
Water to. 20 OZ. 1,000 ccs. 


Wash well after development. Various col- 
oured images can be obtained on the same print 
by local application of the above solutions with 
abrush. This process does not give pure whites. 

Andresen suggested the following modifica- 
tion :-— 


Pyridine base (pure) . 110 grs. 23 g. 
Boiling water IO OZ, 500 ccs. 
then add— 
Sulphuric acid (pure). 180 mins. 37°5 ccs. 
Distilled water Apa yee eae eg aes 


Benzidine sulphate is formed, and partially 
separates out. Cool the solution down to 
100° to 120° F. (38° to 49° C.), and add— 


Sodium nitrite . 
Water : 


in small quantities with continuous stirring. 
The benzidine sulphate is diazotised and dis- 
solves. Filter the solution and pour into five 
times its volume of alcohol, which precipitates 
the diazo compound; filter out the precipitate, 
and dissolve (without drying, as it explodes when 
dry) in— 


Distilled water to . 


The paper or material is sensitised in this cold 
solution by floating or immersion for two min- 
utes, dried in the dark, and exposed under a 
positive, and then developed in a 2 per cent. 
solution of amidonaphthol sulphonic acid —s, 
or amidonaphtholsulphonic acid —9, containing 
2 per cent. of sodium hydrate. Deep blue images 
with pure whites are thus obtained. 

Feer’s process uses aniline diazosulphonate, 
amidobenzols, etc., with phenolic alkalis, 


86 grs. 
Tag: 


18 g. 
50 ccs. 


20 OZ. 1,000 ccs. 


Dichromatic Photography 


amines, and phenylamines, the following being 
typical sensitisers :— 


1. Sodium  toluoldiazo- 


sulphonate - 240 grs. 25g 
B-Naphthol . 4 20, 
Sodium hydrate . 76 ,, Sug 
Distilled water to 20 oz. 1,000 ccs. 
2. Sodium ditolyltetrazo- 
sulphonate - 240 gts. 252g 
u-Phenylendiamin 190 ,, 20°55 
Distilled water to . 20 oz. 1,000 ccs 
3. Sodium ditolyltetrazo- 
sulphonate . 240 grs. 252 
Resorcin , » EET Pee 233 
Sodium hydrate . 154 ,, 16.5; 
Distilled water to . 20 oz. 1,000 ccs, 


The paper is immersed in these solutions, and 
after drying exposed for about five minutes to 
sunlight or electric light. On the exposed parts 
the insoluble azo dye is formed, whilst in the 
unexposed part the sensitiser remains colourless 
and washes out. The print should be fixed in 
hydrochloric acid. 

Andresen discovered in 1894 another diazo 
printing process. The sensitiser is the diazo 
compound of a-naphthylamine or 6-naphthyla- 
mine, the former giving brownish grey images 
and the latter brown-red. If the exposed paper 
is washed amd treated with tetrazo-diphenyl 
ether, violet images are obtained. 


Distilled water . 


heat to boiling, and add— 


B-Naphthyla- 
* . 220 grs. 


Sag, 150 ccs. - 


a- oT 
mine 
then add— 
Hydrochloric acid 
(sp. g. I°19) . 152 gers. 
and as soon as the salt has dissolved add— 
Hydrochloric acid . 617 grs. 40 g. 


with constant stirring, and cool the paste down 
to 40° F. An evolution of gas takes place, and 
a yellowish solution is formed which must be 
filtered into an ice-cold dish. Float paper on 
this for fifteen seconds and dry in the dark. 
Expose for two or three minutes under a nega- 
tive in the sun and develop in a 10 to 20 per 
cent. solution of twice fused acetate of soda, 
and wash well. 

These processes give rather pleasing effects 
when applied to silks and other materials. 


DI-CARBOXYLIC ACIDS (See 
Acids.”’) 


DICHROIC FOG (See “ Fog.’’) 


DICHROMATIC PHOTOGRAPHY 

A process of colour photography invented by 
Gurtner, in which only two constituent colours, 
blue and orange-red, are used. Two plates are 
placed film to film, the nearest to the lens bein 
coated with a transparent emulsion -staine 
yellow ; on this only the blue rays act, and on 
the rear plate, which must be panchromatic, 
the yellow, orange, and red rays act. From these 


14°3 g. 


IO g. 


“* Carboxylic 


Dicyanine 185 


two negatives are made prints, in orange-red 
for the front plate and blue for the rear one, 
and superimposed. Obviously it cannot give 
pure reds or pure yellows, but merely for land- 
scape work some pleasing results have been 
obtained. 

The same principle is used by Smith and 
Urban in kinematography and with far greater 
success, because as the pictures are now pro- 
jected very rapidly, and the observer sits in a 
darkened room, one is not sensible of the absence 
of any colour or the failure to make pure white. 


DICYANINE (Fr. and Ger., Dicyanin) 

Solubilities, soluble in water and alcohol. This 
is a complex aniline dye prepared by the action 
of an alcoholic solution of caustic potash on 
a- ‘y-dimethylchinoline salts with the aid of 
atmospheric oxygen. It forms greenish glitter- 
ing crystals which dissolve in alcohol with a 
greenish-blue colour, and in water with a more 
reddish tinge, both solutions being decolorised 
by acids. It is one of the best sensitisers known 
for the extreme red, particularly for the region 
about A 7,200, the range extending through 
the orange and yellow, but it gives a deep 
minimum or lack of sensitiveness between E 
and F in the green and green-blue, and is not 
therefore so much in use as some of the other 
dyes. It is very easity decomposed in weak 
solution, and therefore should only be added to 
the sensitising bath immediately before use. 
(See also ** Colour Sensitising.’’) 


DIETZLER 

An optician of Vienna, chiefly noted for his 
manufacture of the orthoscopic lens designed 
by Prof. J. Petzval, which was first issued 
in 1858, although calculated as early as 1841. 
(See “‘ Lenses, Orthoscopic.’’) 


DIFFRACTION (Fr., Diffraction ; Ger., Diffrak- 
tion, Ablenkung, Beugung) 

When light passes through a very narrow 
slit it apparently bends round the edges and 
spreads out on both sides. The subject is fully 
gone into under the heading “ Diffraction 
Grating.”’ 

In process work, a theory advanced in regard to 
the action of the ruled screen used for the half- 
tone process is that diffraction plays an import- 
ant part, especially with the finer screens, and 
some authorities claim that advantage can be 
taken of this action to promote the better forma- 
tion of the half-tone dot. Diffraction is said to 

roduce the effect of larger or smaller dot images 
instead of only stronger or weaker ones, as would 
be the case if there were no action of deflected 
light. 


DIFFRACTION GRATING (Fr., Réseau de 
diffraction ; Ger., Diffraktions-Gitter) 

An opaque screen containing a large number 
of fine slits, or a transparent screen having 
opaque lines engraved upon it very close together. 
A pencil of light is formed of a wave front or a 
series of overlapping waves which may be repre- 
sented by the diagram A, in which 1 is the light 
source and aB the main wave front in which 
every particle excites fresh secondary waves, as 
shown by the curve CD. Nearly all these 


Diffraction Grating 


secondary circles mutually interfere one with 
the other, except in the main wave front cp. 
This interference cannot be seen, but its exist- 
ence can be proved by limiting the size of the 
main wave front by an opaque screen $ $s, which 
stops out some of the secondary waves but not 
all, and the latter are seen as delicate fringes 
E F on each side of the main wave front. ‘This 
can be experimentally proved in a very simple 
way. Take a black opaque card about 6 in. or 
8 in. square, and cut in the centre a slit about 
1 in. long and about fin. wide. Take also a piece 
of glass about 3 in. square and either smoke it 
or cover it with black varnish, and with a fine 


AR) 


Vo== 2S OSS 2525 Wy, 
NN meee 


A. Diagram showing Principle of 
Diffraction Grating 


needle-point scratch a thin, clear line about 
$in. long. On holding the card at arm’s length 
close to a brilliant light, and examining it through 
the scratch on the glass, held close to the eye, 
there will be seen a bright central image of the 
slit, and on each side of it faint black lines, which 
are the diffraction fringes. If in front of the 
light source a violet glass is placed and then a 
deep red one, there will be obtained images, as 
shown in the diagram B, in which o is the central 
image, v the violet bands or fringes, and R the 
red ones, the violet being nearer together than 
the red. If a green glass is used the green fringes 
would fall midway between the red and violet. 
The explanation of this phenomenon is as 
follows: In diagram C let AB represent an 
opaque screen with an aperture CD, and 1, the 
beam of light, which, proceeding in a straight 
line, forms a bright central image at EF. Now 
diffraction, or the bending of the light waves 
round the edge of the opaque screen, will cause 
secondary waves to proceed in all directions from 
every particle of ether lying between cp. For 
the sake of clearness, let us consider only the 
waves in one direction, and represent these as 
straight lines CGDH. Let us further assume 
that between c and D there are eight ether 
particles acting as sources of secondary waves. 
If we now draw C w at right angles to the path 
of the rays, it will be at once seen that the 
waves from D have further to travel than those 
from Cc by the distance D w. Let D w be a wave- 
length, then obviously $ Dw is exactly half a 
wave length; drawing a perpendicular from 
4w to the ether particles we at once see that 
the wave from 4 is exactly half a wave length 
from c, and the same distance in front of that 
from D. By the same reasoning it will be found 


Diffraction Grating 


that 1 is half a wave-length in front of 5, 2 
half a wave-length in front of 6, and so on; 
so that every ray is in opposite phase with 
another ray in the slit. Now two rays in oppo- 


site phase (see “‘ Interference of Light ”’) produce 
interference or darkness, so that on the screen 
By similar 


G EHF there would be a dark band. 


B. Diagram of Diffraction Bands or Fringes 


reasoning we could find beyond this particular 
angle a bright band where the secondary waves 
would be in the same phase. 

It is obvious that the greater the number of 
apertures in an opaque screen the greater the 
number of secondary waves formed, and there- 
fore the greater the chance of interference. 
Further than that, the narrower the slit the 
greater must be the obliquity or the angular 
distance from the central image, for the greater 
obliquity will be required to produce the neces 
sary difference between the paths of the rays 
from a narrower slit; that is to say, the more 
slits there are in a unit length the greater the 
obliquity. Now we have already seen that the 
violet bands are closer together than the red, 
and that the green would lie in between, so that 
if we illuminate a series of slits by hetereogeneous 
white light the waves will be sifted out into 
their respective positions, and we obtain a 
spectrum in which the rays are arranged accord- 
ing to their wave length. 

Fraunhofer was the first to utilise the pheno- 
menon of diffraction, and he made his gratings 
of silver wire wound round two fine threaded 
screws placed some distance apart. The next 


ut 


G E H F 


C. Diagram showing Cause of Diffraction 
Bands 


forward step was the ruling of a series of fine 
lines with a diamond on glass, and later still 
the glass was silvered. Then Rutherford, of 
New York, ruled the lines on plane speculum 
metal, and later on spherical mirrors of speculum 
metal. Diffraction gratings on glass are called 
transmission gratings, as the light passes through 


186 


Diffraction Grating Replicas 


them, the rulings acting as opaque screens; 
those on metal are known as reflection gratings. 
Diagram B represents practically the spectra 
which are obtained with any diffraction grating. 
They are arranged on each side of the central 
white image 0. The spectra nearest O are called 
the spectra of the first order, then there is a 


dark space filled by the invisible infra red and 
the invisible ultra violet; then we have the 
spectra of the second order overlapped even in 
the visible spectrum by the violet of the third 
order. Then follow the fourth and other order 
spectra, the number being dependent on the 
brilliancy of the light and the character of the 
grating. 

A moment’s consideration will prove that the 
spectra formed by a diffraction grating cannot 
be as brilliant as a prismatic spectrum, for 
although there is some loss of light with the 
latter, through the reflection from the front 
surface of the prism and by absorption in the 
glass itself, yet in the case of the diffraction 
grating not only does the bulk of the light pro- 
ceed to the central image, which is useless, but 
the rest is split up into the various spectra on 
each side. Sometimes, too, in consequence of 
some peculiarity in the ruling, one or other of 
the spectra may be much more brilliant than 
the others. 

A grating spectroscope or spectrograph is, 
however, much to be preferred to a prismatic, 
as the rays are arranged exactly according to 
their wave-length, whilst with the prismatic 
spectrum the violet and blue are spread out at 
the expense of the red and orange, which are 
cramped together. (See also ‘‘ Spectrum,”’ “ Dif- 
fraction Grating Replicas,” etc.) 


DIFFRACTION GRATING REPLICAS (Fr., 
Replicas des réseaux de diffraction; Ger., 
Diffraktions-Gitter-A bklatsche) 

Original gratings, whether on glass or metal, 
are extremely expensive, and numerous attempts 
have been made by Rayleigh, Abney, and others 
to reproduce these by photographic means, but 
the most successful way is that of taking casts 
in celluloid. Thorpe, Ives, and Wallace produce 
these, and the latter has given full working 
instructions, of which the following is an 
abstract :— 

Pyroxyline . 182 grs. 


. 3°9 &. 
Pure amyl acetate . I oz. 


100 ccs. 

Add the pyroxyline in small quantities to the 
amyl acetate, shake well till dissolved, and allow 
to stand for twenty-four hours. At the end of 
that time the resultant collodion should be 
poured from a height of at least 3 ft. or 4 ft. 
in a very thin stream into a large tray filled 
with water, the latter being constantly stirred 
with a glass rod. In about twenty-four hours 


lela 


Diffraction Grating Replicas 


the whole of the pyroxyline is precipitated in 
the form of white or light grey flocculent masses, 
which should be collected and dried. The pur- 
pose of this precipitation is probably to purify 
the pyroxyline, as any collodion poured into 
water gives up what Eder has called “‘ pyroxyline 
gum.” The particular pyroxyline recommended 
by Wallace is not obtainable in England, 
but Hopkins and Williams’s high temperature 
pyroxyline gives excellent results, as does also 
Mawson and Swan’s collodion when precipitated 
in this way. It is not necessary to use amyl 
acetate before the precipitation, the ordinary 
solvent of equal parts of alcohol and ether 
proving quite satisfactory, and the precipitation 
is instantaneous. When thoroughly dry the 
precipitated pyroxyline is again dissolved in the 
above proportions, and the collodion carefully 
filtered through paper. This, which is trouble- 
some unless pressure is used, may be avoided 
by allowing the collodion to stand three or 
four days, when the whole of the impurities 
settle to the bottom of the bottle. 

The grating should be carefully levelled in a 
drying cupboard, and this is absolutely essential 
to prevent the occurrence of dust; next, it is 
carefully dusted with a soft camel-hair brush, 
and the solution flowed over the surface. The 
exact quantity is a matter of experiment, too 
thin a film being difficult to handle whilst too 
thick a film gives a matt surface. About 1-5 ccs. 
is the right quantity to use for a 2-in. grating. 
The best method of applying the solution is 
with a fine pipette, which will hold just the 
necessary quantity. This enables one to distri- 
bute the solution over the surface without 
touching the grating itself, and the solution can 
be easily led to any part, or an air bubble brought 
to the edge and broken. 

The coated grating should be left in the cup- 
board for at least twelve hours, and longer is 
preferable, even for three or four days; the 
longer it is left the easier it is to handle. To 
strip the cast, the grating should be placed in a 
dish of distilled water, when the edges will soon 
begin to show shadow bands. As soon as these 
are observed the grating should be taken from 
the dish, and any adherent water removed 
with a soft rag. Slight pressure with the thumb 
nail along one edge will cause the cast to spring 
from the metal, and it should then be grasped by 
a pair of wide-jawed forceps, as used in micro- 
scopy, and pulled off with a firm but even 
motion in a direction parallel to the lines of the 
ruling. The edges of the cast should be trimmed 
off, and it should then be lowered on to a piece 
of carefully cleaned and polished plate glass, 
which should be immersed in distilled water 
and lifted out with a small pool of water on its 
surface. One edge of the cast should be lowered 
on to the glass first, and then the rest gradually 
lowered so that it pushes the water in front 
of it without the occurrence of air bubbles. As 
soon as it is in position one edge should be clipped 
by a strong metal clip, and a piece of soft velvet 
rubber passed across it in the direction of the 
rulings; when contact is obtained everywhere 
the edges should be cemented down with some 
of the collodion as used for the cast. This can 
be applied with a very fine camel-hair brush. 
The cast may be cemented face up or face down, 


187 


Diffusion of Focus 


but with the latter there is less chance of the 
tulings being damaged. When the cast has 
been cemented it may be dried by heat, gentle 
at first, but gradually increased to 167° F. 
(75° C.).. The chief cause of failure is dust 
particles between the glass and the replica. If 
the replica is mounted face down, another piece 
of glass may be cemented to the back. 

There is some contraction of the cast in drying, 
but this is small, Wallace found that with a 
grating of 28-867 mm. width and 16,397 lines 
the shrinkage was 0-176 mm. on the entire width, 
or about six lines more to every one thousand. 
The shrinkage can, of course, be easily deter- 
mined by accurate measurement of the original 
gtating and the cast; thus, in the case referred 
to above, the original width = 28°867 mm., 
width of replica = 28-691 mm.; therefore with 
a total of 16,397 lines in the original, 568 lines 
= Imm. On the replica obviously 16,397 + 
28-691 = 572 per mm. This shrinkage simply 
causes greater dispersion of the spectrum. 

When examined in a quartz spectrograph these 
replicas were found to transmit up to A 2,613 
in the ultra-violet, but obviously their glass 
support absorbs up to about A 3,400. Prof. 
R. W. Wood has suggested the use of thin 
mica sheets, and naturally quartz could be used 
for the support. This process of taking casts from 
a grating in no way damages it, it being, in fact, 
an excellent method of cleaning a grating. 


DIFFUSED LIGHT (Fr., Lumiére diffusée ; 
Ger., Zerstreutes Licht) 

Light that is spread and softened by the 
interposition of any translucent medium, such 
as clouds, a misty atmosphere, a muslin screen, 
ground glass, opal, etc.; the opposite to direct 
light, coming unobstructed from the source of 
illumination. Printing in diffused light means 
ptinting in daylight other than direct sunshine. 

Diffused light in the camera, tending to cause 
fog, is light that is reflected or scattered by the 
sides of the camera, etc. 


DIFFUSING SCREEN (Fr., Ecran de diffu- 
sion ; Ger., Verbreitungschirm) 

Synonyms, diffusion screen, diffuser. Any 
translucent material or fabric used to spread and 
soften light. Thus, a frame covered with tracing 
cloth, white muslin, or thin calico is employed in 
the studio to obtain a soft, round lighting. A 
circular diffusing screen is advisable in conjunc- 
tion with: the electric light for portraiture, as 
illustrated under the heading “Arc Lamp.” A 
sheet of ground glass or opal is often used in 
enlarging by artificial light without a condenser, 
to distribute the illumination equally over the 
whole of the negative. The same method is 
frequently adopted in daylight enlarging, though 
an inclined white reflector is perhaps more usual. 
White tissue paper is sometimes pasted over the 
printing frame when a thin negative is required 
to print slowly. <A piece of ground glass in the 
dark-room lamp, behind the ruby or orange glass, 
gives a more even and better distributed light. 


DIFFUSION OF FOCUS 

The soft effect obtained by throwing the 
image very slightly out of focus on the screen 
just before exposure, this producing “fuzziness.” 


Dihydric Phenols 


DIHYDRIC PHENOLS 

Derivatives of phenol or carbolic acid which 
contain another hydroxyl group, thus phenol 
or hydroxy-benzene is C,H, OH, the dihydric 
phenol C,H, (OH),. Catechol, resorcinol, and 
hydroquinone belong to this group, the last- 
named being of much photographic interest. 


DILUTE DEVELOPMENT 

A method in which very dilute developers are 
used, such as in stand development (which see 
under the heading “‘ Development, Stand ’’). 


DIMINISHING GLASS 

A double concave lens mounted in a holder 
and used for examining drawings or photographs 
which have to be reduced by photographic pro- 
cesses. By its use it is possible to judge some- 
what the effect of reduction. 


DINITRO-NAPHTHOL 

Ci»H;(NO,.), OH. The sodium salt is known 
as Martius yellow, which is sometimes used for 
yellow filters. The sulphonic potassium salt is 
known as naphthol yellow. 


DIOGEN (Fr. and Ger., Diogen) 

Solubilities, soluble in cold water, insoluble 
in alcohol and ether. The acid sodium salt of 
a, amido-, 8; naphthol-, 8, 8, disulphonic acid, in- 
troduced in 1897 asa developer. It freely dissolves 
in alkaline sulphite and carbonate solutions, 
giving a yellowish coloured developer, which is 
readily amenable to the influence of a bromide. 


DIOPTICHROME PROCESS 
Dioptichrome Process’’) 


DIOPTRICS 

The department of optics referring to the laws 
governing rays of light passing through trans- 
parent media, as air, water, glass, crystal, etc. 


DIPHENAL (Fr. and Ger., Diphenal) 

CsH;,0HNH, CsHyNH,. Molecular weight, 
200. Solubilities, almost insoluble in cold water, 
very soluble in hot water; soluble in alcohol and 
glacial acetic acid. It must be kept in a well- 
stoppered bottle. It is a highly concentrated 
solution of the phenolate of diamido-oxydiphenyl 
in caustic alkaline solution, and was introduced 
in 1897 as a developer. 


DIPPER (Fr., Crochet; Ger., Kiiwvetienhaken, 
Silberhaken, Platienheber) 

A kind of holder employed in the wet collo- 
dion process, to immerse the plate in the silver 
bath. It may be of glass, porcelain, ebonite, 
or silver wire, and is furnished with hooks or 


(See “ Dufay 


A. Fluted Glass Dipper 


projections at the bottom to hold the plate. 
Those of fluted glass A, though somewhat liable 
to breakage, are perhaps the cleanliest. 

In process work, where the dipper is important 
for the wet-plate process commonly worked, 
various forms have been adopted. The usual 


188 


Direct Finder 


styles are the fluted glass A and ebonite B. The 
forked dipper C is an American idea, the object 
being to support large plates more firmly than 
do the usual narrow dippers. Another kind of 
dipper is made of hickory wood; by pressing 
the handle parts together the forks move apart 


C. Forked Dipper 


and allow the plate to be inserted. On releasing 
the pressure the forks press the plate between 
them, so that there is no chance of dropping 
it. A coat of shellac varnish makes the wood 
waterproof. A similar arrangement can be 
used as a developing holder. Silver wire or 
silver plate can be bent to the shape of a dipper, 
but becomes expensive in large sizes. 


DIPPING BATH (Fr., Cuvette verticale a bain 
d’argent ; Ger., Kuvette) 

The upright vessel of ebonite, glass, etc., for 

containing the silver bath in the wet-plate pro- 

cess. Those made of white glass are preferable. 


DIPPING-BATH DEVELOPMENT 

An early form of what is known as stand 
development. It was advocated in 1892 by a 
German, Dr. A. Meydenbauer, who described it 
under the name of ‘“‘Standentwickelung.” Its 
principle is found in the prolonged action of a 
very diluted developer contained in a dipping- 
bath. The early name “ dipping-bath develop- 
ment’’ has been superseded by “‘ stand develop- 
ment’; for full particulars, see ‘Developing 
Tank” and ‘‘Development, Stand.” 


DIRECT FINDER, OR DIRECT-VISION 
FINDER (Fr., Viseur direct; Ger., 
Divektsucher) 

A finder in which the view or object to be 
photographed is inspected direct, the camera 


A. Full-sized Direci-vision Finder with 
Wire Frame 


being held up to the level of the eye. The full- 
sized direct-vision finder A consists of a rectangu- 
lar wire frame C the size of the plate used, and 


Direct Positives 


having a small opening or sight B fixed at a 
distance from it equal to the focal length of the 
lens with which the camera is fitted. If the 
sight is at the correct height, the eye placed 
against it will see through the frame the exact 
view included on the plate. The frame and 
sight are either detachable or made to fold 
down when not in use. When the camera is 
not of fixed focus, the frame should be attached 


B. Direct Vision Finder with Lens 


above the lens, so that it may move with it, 
to suit different extensions and to agree with any 
rise or fall given to the front. Another form of 
direct finder B consists of a concave lens, the 
sides of which are trimmed to a rectangular 
shape, with a small sight to indicate the dis- 
tance at which it must be inspected. This 
gives a small but brilliant image. Cross lines 
are usually marked on the lens to assist in hold- 
ing the camera level. 


DIRECT POSITIVES (See “‘ Positives, Direct.’’) 


DIRECTOSCOPE 
A stereoscope for the direct observation of 
colour (screen-plate) transparencies without 


reversal; invented and patented by M. G. 
Balmitgere in 1911. 


DISGUISING THE CAMERA (Fr., Déguisement 
de la chambre ; Ger., Camera verstellen) 

In detective work it is frequently necessary 
to conceal the presence of the camera. This 
may sometimes be done by causing it to resem- 
ble some other article, such as a brown-paper 
parcel, a bundle of books, a brief bag, an opera 
glass, etc. A box-form magazine camera is 
easily made to look like a parcel by wrapping 
it somewhat carelessly in brown paper and tying 
with string, to which a luggage label may be 
attached. Holes should be torn for the lens 
and finder, leaving, however, a flap of paper 
hanging loosely over them to hide them until 
actually wanted. Many special forms of cam- 
eras have been made for purposes of disguise, 
such as one to work behind the waistcoat of 
the operator, the small lens protruding through 
a buttonhole; an apparatus for concealment in 
the hat; another resembling a lady’s reticule, 
and so on. 

Sometimes, in natural history photography, it 
is required to prevent animals, birds, etc., from 
knowing of the camera’s proximity, and there 
are many ways in which this may be done, It 
may, for instance be hidden by an arrangement 
of boughs and twigs, or a moss-covered heap of 
stones, and possibly operated from a distance 
by a pneumatic or electric release. The precise 
method chosen depends on the nature of the 
surroundings. Considerable patience is called 
for, and it is not unusual for the operator as 
well as the camera to be completely concealed. 


189 


Dissolving Chemicals 


DISHES (Fr., Cuvettes, Cuves; Ger., Schalen, 


Tassen) 
Dishes are described under the heading 
** Baths.”” (See also ‘‘ Cleaning Dishes.’’) 


DISINFECTANT 


Any substance which kills bacteria and 
microbes, such as carbolic acid, formaline, corro- 
Sive sublimate, etc. Rapid oxidisers, such as 
potassium permanganate, also act as disinfectants. 


DISPERSION 


streuung) 


The breaking up of white light into the 
various colours forming the spectrum, as seen 
when a prism is interposed in the path of a 
beam of light proceeding from a narrow opening 
or slit. Sir Isaac Newton was the first, in 1666, 
to show that rays of various colours have differ- 
ent refrangibility. The shorter the wave-length 
of the light the greater is found to be its refrangi- 
bility ; thus red rays, which have the longest 
wave-length, are less refracted than the violet 
rays, which have the shortest wave-length. 
The same law applies to the non-visible infra- 
red and ultra-violet rays, at opposite ends of 
the visible spectrum. There are, however, a 
few cases in which the law is departed from. 
If, for instance, fuchsine is prepared in the form 
of very thin prisms, it produces a spectrum in 
which the red and yellow rays are more refracted 
than the blue and violet. This phenomenon is 
known as anomalous dispersion. 

Newton predicted that dispersion could not 
be eliminated without at the same time losing 
the property of refraction. This is now known 
to be erroneous, since different kinds of glass 
may give practically the same amount of dis- 
persion, yet have varying refractive properties. 
It is thus possible, by combining lenses made of 
dissimilar kinds of glass, practically to neutralise 
the effects of dispersion, a lens in which this 
is done being known as achromatic. (See 
also ‘* Lens.’’) 


DISSOLVING CHEMICALS 

There is a right and a wrong way of dissolving 
and mixing most chemicals, and in some cases 
the method of dissolving affects the working 
powers of the solution. The slowest and possi- 
bly the worst way of dissolving a chemical is to 
place it in a bottle of liquid and let it stand. 
The quickest way is to have the salt, particularly 
soda, near the surface of the water and suspended 
therein in a canvas bag. However, for most 
solutions, the simple addition of chemicals, when 
not in large quantities, and frequent shakings 
will be sufficient. Chemicals usually dissolve 
more quickly in hot water than in cold, though 
there are some notable exceptions to this rule. 
(See ‘* Solubilities.’’) 

The order in which chemicals are dissolved 
or mixed has its influence on the working and 
keeping qualities of the solution. As a general 
rule, ingredients are added in the order given in 
the formule, otherwise special instructions are 
given. The following general hints should be 
noted :—Metol should be dissolved in the water 
before any other chemicals are added. Hydro- 
quinone should always be dissolved after sodium 
sulphite. When pyrogallic acid is used, the 


(Fr., Dispersion; Ger., Zer- 


Dissolving- Views 


preservative—acid, metabisulphite, etc.—should 
be dissolved in the water before the pyro. When 
gold toning baths are made, the gold should 
always be added last, dissolved in water. Sul- 
phuric acid should always be added gradually to 
the water and not water to the acid, otherwise 
combination takes place so energetically as almost 
to resemble an explosion, and some of the acid 
may be driven in the face or over the clothes. 
The list of solubilities presented in the table 
that is given under the heading ‘“‘ Solubilities’”’ 
will assist in deciding whether much advantage 
will be gained by using hot or cold water. 
In some cases the temperature of the water 
is not of much importance. Developers such 
as pyro, metol, adurol, etc., are best dissolved 
in water that has been well boiled in order 
to get rid of the air, and then allowed to cool 
slowly. 


DISSOLVING-VIEWS 

These are obtained by the use of two lanterns, 
ene above the other, or placed side by side. The 
discs of light projected by the two lanterns must 
coincide. Whilst a picture is being shown in 
the first lantern, the illuminant is quite low in 
the second one. A slide is placed in the second 
lantern, and then the light of the first one is 
gradually lowered whilst that of the second one 
is gradually turned up; the first picture dis- 
solves away during the blending of the lights, 
and at the same time the second picture makes 
its appearance on the screen, taking the place 
of the first. To facilitate the operation (especi- 
ally when lime-light is in use) the rubber tubing 
from the two jets is connected to a duplex gas- 
cock having four ways or channels, through 
which the gases may be made to pass. ‘Thus, 
the oxygen and hydrogen of one illuminant is 
partially diverted or reduced, whilst the tap 
allows a full supply to pass to the other jet. 

Dissolving effects are sometimes produced 
with bi-unial lanterns with their objectives 
furnished with iris-diaphragms opened and 
closed alternately. This method is very effec. 
tive, and saves having to interfere with the 
adjustment of the illuminants. 

Dissolving effects of a kind may be produced 
by means of a single lantern. The special 
carriers for obtaining such effects are divided 
into two classes. In one, a translucent screen 
gradually obscures the light, and just at the 
moment when the obscurity is complete, the 
slide is quickly changed by means of a carrier 
of the “to and fro” type. In another class, a 
second slide is pushed into a carrier which already 
holds a slide that is being shown; the second 
slide passes in front of the first, the latter is 
withdrawn, and then, by means of a spring, 
the ont-of-focus slide is quickly pushed back 
into the place previously occupied by the first 
slide. This form of carrier was invented by 
R. R. Beard, and still enjoys popularity. 

Dissolving effects in kinematograph pictures 
may be produced in two ways. If it is desired 
to make provision for such effects at the time of 
taking the original negative film, it is accom- 
plished as follows: An iris-diaphragm, capable 
of completely closing at the centre, is fitted to 
the camera lens, and a short length of film is 
sun through at the commencement whilst the 


190 Distance Meter 


iris is completely closed. Proceeding to wind 
through the film, the iris is gradually dilated 
and finally brought to its full aperture. The 
effect upon the sensitive emulsion is that the 
image of the object to be photographed fails to 
impress itself at first, and as the aperture enlarges 
in the iris, the film is more and more impressed, 
till at full aperture a full exposure is secured. 
Fhe negative is then developed in the usual way. 
Such a negative will yield a positive in which 
the image gradually grows in strength, and as, 
at the commencement, no image will be seen, 
on projection the subject upon the screen will 
appear to develop out of thin air. If the image 
is intended to dissolve away and thus give 
place to a different subject, the iris on the 
camera is closed gradually whilst continuing to 
wind the film. ‘Thus, a reverse effect will result 
when the negative is printed. Any subject may 
be treated in a similar way at the printing stage 
by regulating the illuminant used whilst print- 
ing. Thus, at the commencement, the light is 
kept very low, and as the films pass through the 
printer the illuminant is gradually turned full 
on till sufficient light is produced to secure 
normal exposure. Yet another method is to 
keep the illuminant at a uniform brilliancy and 
to regulate the exposure by modifying the 
speed at which the films are wound through the 
apparatus, 

To make one kinematograph subject dissolve 
gradually into another, double printing is 
resorted to. At that point where the first print 
commences to weaken, through reduced expo- 
sure, a second negative (of the second subject) 
is placed in contact and gradually printed up, 
till it reaches full vigour. Hence, instead of one 
subject dissolving away entirely before a second 
begins to make its appearance, the image of the 
second subject will make its appearance, weak at 
first, but gradually growing in strength and 
finally becoming of full vigour, and this whilst 
the preceding image melts away. 


DISTANCE 


That part of a picture farthest from the 
spectator, and generally quite subordinate to 
the rest of the view, to which, however, it must 
stand in proper relation. Occasionally it forms 
the mentite the subject. When a bluish dis- 
tance is desired stronger than it would appear in 
the ordinary way, an orthochromatic plate with 
a deep yellow colour filter will be of great assist- 
ance. In telephotographic work it is often 
difficult, and sometimes impossible, to render 
distant objects clearly even by such means, on 
account of the interposition of large volumes 
of air of varying density. 


DISTANCE METER, OR TELEMETER (Fr., 
LTéléméive ; Ger., Entfernungsmesser, Dis- 
tanzmesser) 

An instrument for estimating the distance 
of an object from the camera, so that it may be 
accurately focused by means of the focusing 
scale, without having to inspect the image on 
the screen. In one form A the distance is 
indicated on a scale by a small pendulum in the 
shape of a pointer. The appliance is held up 
to the eye, so that the latter looks along the 
sights towards the base of the object to be 


Slal n , 


Distance Scale 


photographed. The index then shows the angle 
made by the line of sight with a perpendicular 
drawn to the observer’s feet, which angle varies 
with the distance of the object. By pressing 
slightly with the forefinger on the top of the 
pendulum it is prevented from moving when the 
telemeter is lowered for examination. Another 
type of distance meter consists of a small tele- 
scope which indicates the distances on which 
it is focused. In the pattern illustrated at B, 


— ee 


 — Whi Wiss 
= @| i ie 
—— 


S= E 


il | 
ie) i at thy 


Aand B. Two Forms 
of Distance Meter 


the instrument has first to be fully extended 
and the eyepiece focused correctly on the grain 
of the ground glass inside the telescope. The 
eyepiece tube is then scratched with a knife, 
so that the observer may always in the future 
be able to secure the focus suited te his particular 
vision. This having been adjusted, the object 
glass is revolved until the object to be photo- 
graphed is seen sharply on the ground glass. 
The arrow will then point to the correct distance 
of the object on the engraved scale. 


DISTANCE SCALE (See “ Focusing Scale.’’) 


DISTILLED WATER (Fr., Eau distiliée ; Ger., 
Destilliertes Wasser) 

Pure water, obtained by vaporisation in a 
still and subsequent condensation of the vapour. 

Distilled water is advised for many chemicals, 
and as it may be obtained so very cheaply from 
a chemist, it should be used when recommended, 
and most certainly for such chemicals as gold 
chloride, silyer nitrate, and uranium nitrate, 
which are both expensive and prone to decom- 
pose in water containing impurities. Whether 
distilled water should be used for all developers, 
toners, etc., depends upon the character of the 
ordinary water available. With many of the 
common chemicals used in photography—all 
sodiums, potassiums, etc.—tap or other water 
good enough to drink will serve quite well. 

In process work, distilled water is used in 
large quantities for making up the silver bath. 
The use of tap water is possible, but it occasions 
some amount of trouble. 


DISTORTION (Fr., Distorsion; Ger., Verdre- 
hung) ‘ 

It is a common error to attribute every un- 
pleasing effect in the “‘drawing”’ of a photo- 
graph to distortion, but, as a matter of fact, true 
distortion is very limited in photography. The 
most common and the most serious form is 
known as curvilinear distortion, and is con- 
fined to single lenses and to certain forms of 
compound ones. In the case of the single lens 
this distortion is shown by a bending of the 
lines, which becomes more pronounced towards 
the edges of the field, the bending being out- 


191 


Dolland’s Process 


wards from the corners when the diaphragm is 
used in front of the lens, and inwards when 
the diaphragm is placed behind the lens. (See 
“‘ Curvilinear Distortion.””) Distortion by con- 
vergence of straight lines is treated under the 
heading “Swing Back.’’ Violent perspective, 
which is sometimes wrongly called distortion, is 
quite distinct from it. If a photograph taken 
with a rectilinear lens, however wide its angle 
may be, is tested by the inflexible rules of 
plane perspective, it will be found to be correct, 
no matter how ridiculous it may appear owing to 
the choice of too near a standpoint. 


DIVERGENT RAYS 


Practically all the light which the eye sees 
or which enters a lens is composed 
of divergent rays. Every point in 
an object emits rays which diverge 
in all directions from which it is 
visible, and the lens of the eye or 
of the camera causes them to con- 
verge and form an image. When an object is 
extremely remote the degree of divergence is 
very small, and such rays are termed parallel. 


DIVERGING LENS 


A concave lens, or one which is not capable 
of producing an actual image. It is often called 
a “negative’”’ leus. The magnifying element 
of a telephoto lens belongs to this class, 


DIVERSITY 


In pictorial composition, the introduction of 
many varied objects each claiming more or less 
attention. Unless kept strictly within bounds 
it results in confusion. 


DIVIDING BACK (See “‘ Repeating Back.’’) 


DODGING NEGATIVES AND PRINTS (See 
“Control in Printing.’’) 


DOLLAND’S PROCESS 

A method of toning and intensifying platino- 
type prints, worked out by A. W. Dolland. Its 
advantages are that it strengthens a weak 
platinum print, and at the same time changes 
it to a pure black or blue-black colour. ‘The 
weak black picture to be strengthened and 
toned—the more recently made the better, as 
rints more than about ten weeks old are diffi- 
cult to treat—is soaked in warm water and then 
laid face upwards on a sheet of warm glass. All 
superfluous water is blotted off, and a thin 
covering of glycerine is gently spread over the 
sutface by means of the finger-tip or a broad 
camel-hair brush. A strong solution of gold 
chloride (15 grs. to 74 drms. of water) is then 
made up, and a few drops of it brushed over the 
glycerine-covered print as evenly as possible. 
The print soon begins to gain strength, and at 
the same time the colour of the print gradually 
changes to a warm black, then cold black, and 
finally blue-black. As soon as the desired effect 
is attained the print is well washed in water 
in order to remove the gold and glycerine, care 
being taken during the treatment with gold 
that the high lights remain unaffected. After 
washing, and in order to ensure the reduction 
and elimination of any gold compounds which 


Donisthorpe Process 


are liable to be formed with the sizing of the 
paper, the toned print should be sponged back 
and front with any clean-working alkaline 
developer, the formula specially recommended 
by Dolland being : 


A. Metol. 


: . 100 grs. Io g 

Sodium sulphite. 2 ,, 100 ,, 
Water to 20 OZ. 1,000 ccs, 

B. Potass. carbonate 240 grs. 24 &. 
‘Water to 20 Oz. 1,000 ccs, 


Use equal parts of A and B, and finally wash 
for about a quarter of an hour. All the above 
operations are best carried out in the strongest 
daylight possible. 


DONISTHORPE PROCESS 

A printing method, invented by Donisthorpe, 
in 1908, a modification of the old hydrotype 
process. A negative is taken in the ordinary 
way and after developing, fixing, and washing 
is immersed in a mixture of vanadium chloride, 
potassium ferricyanide, ferric chloride, and 
oxalate. The silver image is probably converted 
into chloride and ferricyanide and dissolves, 
whilst vanadous salts are precipitated in situ 
which harden the gelatine. After washing, the 
negative is immersed in aniline dye solutions 
which are absorbed by the hardened gelatine, 
and not by any unchanged gelatine; the dye 
is finally removed by absorption by a film of 
damp gelatine, thus obtaining a print. After 
one print has been made, the negative is again 
dyed for a few minutes, rinsed, and another 
impression is taken. 


DOPPLER’S PRINCIPLE 

A principle discovered by Doppler, by means 
of which it is possible to tell with considerable 
accuracy the rate of travel of a star to or from 
the earth. It being assumed that a star at a 
fixed distance emits light waves of a given 
length at a uniform rate, it is obvious that the 
number of ether waves striking the observer's 
eye will be constant in a given time. If, on the 
other hand, the star be travelling away, fewer 
waves will meet the observer’s eye in a given 
time, as the waves have further to travel. The 
converse naturally holds good with a light 
source travelling towards the observer. Now, 
if fewer waves strike the eye in a given time, the 
wave-length must be increased, whereas if more 
waves strike the eye the wave-length is decreased. 
In the first case the monochromatic light would 
incline towards the red, and in the latter case 
more towards the violet end of the spectrum. 
The displacement is naturally dependent on 
the velocity of movement of the light source, 
and this is usually measured for the F or H Bline, 
and taking the velocity of light as 299,860 kilo- 
metres per second, it is obvious that about 
61 kilometres per second would result in an 
increase or decrease of 1 Angstrom unit in the 
wave-length of this line. 


DOT FORMATION 

An expression used in relation to the half- 
tone process when describing the dot effect 
produced by photographing through the ruled 
screen. The ideal dot formation is such that 
in the deepest shadows of the negative (the 


192 


Double Exposures 


most transparent parts) the dots are reduced 
to mere pin points, and as the tones deepen 
towards the highest lights (the darkest parts of 
the negative), the dots grow in size until they 
join together and leave small transparent open- 


Gradation Showing Ideal Dot Formation 


ings between. Above is shown a diagrammatic 
representation of the ideal dot formation. 


DOUBLE CONCAVE (See “ Biconcave.’’) 
DOUBLE CONVEX (See “ Biconvex.’’) 
DOUBLE DARK-SLIDE (See ** Dark-slide.’’) 


DOUBLE EXPOSURES 


Two exposures may be made on one plate— 
each one filling half the plate—by having a shield 
of metal or thin wood fitted to the camera back 
close to the dark slide. The shield covers half 
of the plate while the other half is exposed ; 
then the position of the shield is changed so that 
for the next exposure it covers the exposed 
half while the second half is exposed. The 
shutter of the slide may be drawn right out for 
each exposure; the shield forms a perfect pro- 
tection for the part covered. By means of such 
a fitting a half-plate may be used for two quarter- 
plate exposures. 

A few years ago this method of making two 
exposures on one plate was very frequently used 
by amateur photographers for producing a type 
of portrait that could not be attained by any 
other method excepting combination printing. 
(See ‘‘Doubles.”) Another form of double 
exposure is that which is frequently utilised for 
obtaining “spirit”? or “‘ ghost”? photographs. 
A plate is exposed in the usual manner on the 
subject in which it is intended that the “ ghost ”’ 
should appear. The lens is capped while the 
figure that is to form the ghost is introduced. 
Then a short supplementary exposure is made, 
care being taken to avoid moying any part 
of the subject between the two exposures. A 
transparent shadowy image of the added figure 
will appear, solid objects in the picture being 
visible through it, 

An annoying form of double exposure is that 
obtained by exposing the same plate twice, by 
accident. The best method of avoiding this is 
to make it a rule to change the plate immediately 
after exposure when using a magazine hand 


YELLOW 


A FOUR-COLOUR PRINT 
AND THE 
CONSECUTIVE STEPS 


IN ITS PRODUCTION 


BLUE 


RED 


YELLOW + RED + BLUE + GREY 


YELLOW + RED + BLUE 


YELLOW + RED 


The original, of which this is a 

small portion, is an Autochrome 

Photograph by H. ESSENHIGH 
CORKE, F.R:-F:S: 


Especially taken for “Wild Flowers 
as They Grow” 


GREY 


Double Extension 


camera, and to expose all plates in rotation 
according to the number on the dark-slides 
when these are employed. 


DOUBLE EXTENSION (Fr., Double tirage; 
Ger., Doppel Ausdehnung) 

A camera is said to be of double extension 
when its construction allows the racking-out 
of the bellows to about twice the focal length 
of the lens that is fitted. The usual arrange- 
ment consists of an ‘‘ extension frame’’ sliding 
in grooved rails on the baseboard, and worked 
by a rack and pinion. When two extension 
frames are provided, allowing the bellows to 
be racked out to about three times the focal 
length of the lens, the camera is said to be of 
triple extension. The advantages of a long 
extension are that near objects may be success- 
fully photographed, copying done full size or even 
larger, and telephotographic work undertaken. 


DOUBLE IMAGES 

A double image on a negative is the result 
of one of two causes. Hither the camera has 
moved during the exposure, or else the subject 
has moved. If the latter, any moving part of 
the subject will show a double outline, while the 
remainder of the subject will be sharp. If the 
whole of the image is doubled, it indicates 
movement of the camera, laterally or vertically, 
according to which outlines show the movement. 

A double image in a print, if the negative is 
sharp, indicates that the paper has moved during 
printing, due to want of care in examining. 


DOUBLE PRINTING (See 
Printing.’’) 
DOUBLE REFRACTION 
When a ray of light passes through certain 


materials it is not only refracted but divided 
into two parts, one of which, called the ordinary 


“ Combination 


tay, obeys the ordinary laws of refraction, while 


the other, or extraordinary ray, does not. The 
most usual method of exhibiting this phenomenon 
is to place a cross or other figure behind a slab 
of Iceland spar, when it is seen to be duplicated. 
The polarisation of light depends upon double 
refraction. (See ‘‘ Polarised Light.’’) 


DOUBLE TONES 

In silver printing these are frequently a source 
of trouble. Owing to the lighter portions of the 
subject toning more rapidly than the darker 
ones, the light parts will be quite cold in tone, 
a blue-grey, while the shadows may still remain 
a brick red; for, as a general rule, when the 
light parts begin toning at a more rapid rate 
than the shadows, they continue in the same way 
throughout the operation, the shadows taking 
comparatively little gold. This defect most 
frequently arises from one of two causes. Either 
the toning bath is too weak, or there is too small 
a quantity of gold for the prints in hand. The 
combined toning and fixing bath does not give 
double tones. 


DOUBLE TONING 
This is a method frequently adopted in silver 
ptinting for obtaining tones that cannot be 
secured by a single bath. Almost any chloride 
13 


193 Doubles 


emulsion printing-out paper will give fine black 
or brown-black tones by first toning with gold 
and then with platinum. A simple and satis- 
factory method of working is to use a self-toning 
paper. The prints should be washed, toned with 
platinum, and then fixed, preferably in a fixing 
solution that has been rendered slightly alkaline 
with ammonia. A good toning formula is :— 


Potassium chloroplatinite 3 grs. . °3 g. 
Sodium chloride ? BO fe a. 
Citric acid ° : SOc) ae Ce 
Water to 20 OZ. 1,000 ccs. 


An entirely different double toning is that of 
toning bromides and lantern slides to two dis- 
tinct colours. (See ‘‘ Lantern Slides, Two-colour 
Toning of.’’) 


DOUBLE TRANSFER 


A term used in the carbon process to describe 
the method of working when the reversed print 
given by the ordinary single transfer method 
is inadmissible. The print is transferred first 
to a temporary support on which it is held dur- 
ing development. (See “Temporary Support.”) 
After drying it is transferred to a paper which is 
to be its final support, and it is the necessity for 
this second transfer that gives it the title of 
double transfer. (See also ‘‘ Carbon Process.’’) 


DOUBLES 


A popular form of freak photograph, showing 
two pictures of the same person on one plate, 
as, for example, a man playing cards with himself, 
etc. This kind of picture was at one time (1880) 
somewhat popular among professional photo- 
gtaphers, but the work is now almost exclu- 
sively confined to amateurs. Each half of the 
plate is exposed separately, thus allowing the 
figure to be taken twice on the one plate. Many 
methods of making such exposures have been 
advocated and a few accessories placed on the 
market, but excellent doubles may be made 
with the simplest of fittings. 


Cardboard Cap to Lens, Used in Producing 
Doubles 


For the partial lens cap method a lens cap is 
made of blackened cardboard, as A, the ring c 
being made to fit easily the front of the lens, 
and then covered on one side with blackened 
cardboard B from which a segment is cut off as 
shown at a; exactly how much to be cut away 
should be found by trial. Having cut away a 
very small portion, the partial cap is placed on 
the lens and the picture examined on the 
ground glass. The cutting away must be con- 
tinued until one half of the picture is dark and 
the other half lighted. The dividing line as 
seen on the screen will not be cleanly cut, but 
will have a diffused or vignetted effect. About 


Doubles 


the proportion shown on the right-hand side 
will have to be cut away, certainly not one half 
of the card, as might be supposed. During the 
cutting, the cap is revolved on the lens mount 
so that both halves of the view can be seen, and 


<- a 
S 
N 
. 
N 
S 
N 
x 
Vy! 
N 
: 
S 
N 
N 


2 


SSSA CEOS SOS 
SS S (2 


% 


D. Card in Reversing Back 


when one half vignettes or merges into the other 
a trial plate may be exposed. It requires accu- 
rate cutting to allow of one exposure merging 
into the other, and to prevent the join between 
the two separate exposures being distinguished. 
If, for example, a thin under-exposed band 
shows down the centre of the plate the covering 
part B is too large, and not enough has been cut 
away; if, on the other hand, there is a dense 
over-exposed strip, the aperture a is too large, 
thus causing the centre to receive a double 
exposure. To use the cap, it is placed on the 
front of the lens with the opening on the right- 
hand side, as in B, and the sitter is then 
posed and focused on the half (left hand) of the 
screen on which the picture is seen, exposure 
shutter set, dark-slide put in, and the exposure 
made in the usual way, the shutter of the dark- 
slide being drawn out all the way. For the 
second half, the camera must not be moved, 
the slide is closed, taken out, and the partial 
cap revolved to the opposite side—that is, to 
the position shown at C. The sitter then 
assumes a position that will be visible upon the 
second half of the focusing screen, the partly 
exposed plate is.again inserted in the camera, 
and the second exposure made on the unexposed 
half of the plate. Obviously the two exposures 


eee 
UAIILOLIIOTETID ds 
Y 


| 


Sliding Front. | 
| 1 


ill 


E. Box to Fit on Camera Front 


must be of exactly the same duration. For this 
method the camera must be provided with a 
shutter working behind the lens. 

If the camera has no shutter, and exposures 
are made by removing the cap, a cut cap cannot 
be used. The circular card from which the 


194 Dram, or Drachm 


segment has been cut off, and without a ring, 
can be fitted into the lens hood itself, and of 
course covered over with the ordinary cap with 
which the exposures are made. 

Another favourite plan of making doubles is 
to fix a card in the reversing back of the camera 


(see D), the card being blackened and of a size 


to cover one half of the plate. The first exposure 
is made with the card at B, so as to photograph 
the half marked a; the card is then removed 
to A in order that the remaining half of the plate 
B may be exposed. The card used at the back 
needs to be cut even more accurately than that 
used in the lens, because being so near the 
plate the dividing line between the two expo- 
sures is more clearly cut. It is desirable to 
select a background with vertical lines which 
will not clearly show the division—a bookcase 
or a door, for example—and the inevitable line 
between the two parts of the image is so arranged 
that it coincides with a strongly-marked natural 
line in the view. 

Another accessory (somewhat analogous to 
the first method described) is shown at E. 
This is a box of very thin wood, blackened 
inside, about 6 in. long, 3 in. deep, and 4 in. 
high; it has a round hole cut in the centre of 
the back part so that it may be fitted on the 
front of a lens and used as a kind of partial 
lens cap. The front of the box is fitted with a 
sliding panel or half lid, which slides across the 
front in grooves, allowing each half of the plate 
to be exposed in succession. Over all there is 
a proper lid which serves as a cap. This box 
front is used after the manner of the partial 
cap, and the exact width of the sliding panel 
can only be found by experiment as before, 
one side of the sliding panel being cut accord- 
ingly. The latter may be worked by a knob 
on the centre of the panel itself, or by means of 
a wire. 

In all cases it is advisable to arrange the whole 
scene first, and to allow the sitter to try both 
positions, examining the ground glass carefully 
to see that all is included, and that no, part 
of the sitter—feet and. legs, for example—gets 
beyond the centre, or the whole effect may be 
spoilt. 

A style of “double” portrait (two or more 
positions at one sitting and with one exposure) 
is that known as a “ polypose portrait.” 


DOUBLET 

An old term used to denote a double com- 
bination lens, and usually composed of two 
cemented meniscus lenses. The ordinary por- 
trait lens is classed as a doublet. The rapid 
rectilinear may be considered the typical doublet. 


DRAGON’S-BLOOD (See ‘‘ Gums and Resins.’’) 
DRAINING RACK (See “‘ Drying Rack.’’) 


DRAM, OR DRACHM 

In apothecaries’ weight 60 grs., or one-eighth of 
an ounce; in avoirdupois weight 2744 grs., or 
one-sixteenth of an ounce. In fluid measure 
one dram is 60 minims, or one-eighth of an 
ounce. The French equivalent to one dram 
(fluid measure) is 34 cubic centimetres. (See 
“Weights and Measures.’’) 


Draper, John William 


DRAPER, JOHN WILLIAM 

Born at St. Helens, Lancs, 1811; died on the 
Hudson River, 1882. Anglo-American author 
and scientist. Went to America in 1833 and 
became professor of physical sciences in Hamp- 
den Sidney College, Virginia (1837), and pro- 
fessor of chemistry in the University of New 
York (1839). He made researches into the 
chemical action of light, radiant energy, spec- 
trum analysis, and photography. In 1839 
(details published March 31, 1840) he was the 
first to make a portrait of a living person, the 
subject being his sister Dorothy Catherine 
Draper, whose face was made white by powder- 
ing and given an exposure of about half an hour 
in bright sunlight. Draper was also the first 
to photograph the moon (March 23, 1840); 
it was necessary to give an exposure of twenty 
minutes, a daguerreotype plate being used. 


DRAPERY FOR FIGURE SUBJECTS 

Portraits of draped subjects are popular with 
photographers chiefly because drapery offers so 
many opportunities for artistic treatment, being 
often more pleasing than everyday dress, which, 
more particularly in the case of feminine gar- 
ments, goes so quickly out of fashion. As 
regards the material and colour of drapery, 
opinions largely differ; some photographers use 
ordinary muslin, others a cheaper fabric called 
tarlatan, while a few favour bunting and silk 
shawls. Cheese-cloth is probably the best 
drapery for the figure, and muslin for the head. 
The material used should not be quite new, and 
should have been washed, wrung out and rough 
dried; new materials contain too much stiffen- 
ing to allow of their following the lines of the 
figure properly, and this is particularly the case 
with tarlatan, which needs a thorough washing 
in hot water to adapt it to the purpose. White 
flimsy material photographs too white in ordinary 
lighting, and it is therefore better to make it 
slightly dingy or less actinic by dyeing a pale 
yellow colour, by steeping it in coffee, or by 
allowing it to become somewhat soiled with 
usage, 

Blue, yellow, and even black muslins are also 
advocated by many workers, but strong blues 
and yellows should be weakened by rinsing in 
water and hanging in the sunshine to rough 
dry. The lines of the figure show very well 
indeed through thin dark muslins, and good 
effects are obtainable by draping a thin white 
material over a dark one; but in all cases of 
head and shoulder drapery more depends upon 
the softness and the character of the lighting 
than upon the actual composition of the material. 
Upon the lighting, exposure, and development 
depends whether the material will photograph 
the same tone as the flesh. 

Drapery for the full length figure need not 
be so thin as that used for head and shoulder 
studies. Muslin and tarlatan are available, but 
cheese-cloth is much more amenable to the 
production of artistic folds, the choice largely 
depending upon whether the more or less dim 
outlines of the figure are required to show or 
not. No attempt should be made to reproduce 
the lines of orthodox clothes with cheese- 
cloth, the best effects being obtained by, as it 
were, hanging the material upon the figure or 


195 Drawings, Copying 


by imitating the ancient Greek style. One of 
the many ways in which the Greeks differed 
from all other ancient peoples was in their 
method of covering their bodies. They did not 
make what may be rightly called clothes; 
apparently they cut the cloth to the proper 
sizes, hemmed the ends, decorated the pieces 
with lines of coloured embroidery, and sewed 
on buttons. To make a serviceable cheese- 
cloth garment in the Greek style, and suitable 
for full-length female figures, the width of the 
piece must be, for the long and flowing principal 
garment, equal to the height of the model. If 
seams are unavoidable, let them run vertically, 
they can then be more or less hidden in 
the folds. The width of the principal garment 
must be equal to double the distance between 
the extended finger-tips; the width will thus 
be found to be ordinarily a little more than 
twice the person’s height. Fold the piece ver- 
tically. Next, on each side of the centre, and at 
such a distance apart as to leave an opening 
for the head, place a button and button-hole ; 
this opening should be the width of the model 
across the shoulders. Along the upper edge 
other buttons or hooks and eyes may be placed 
at about 2 in. intervals extending to the ends. 
This garment, put on over the head, has a closed 
side at the left, leaving the right open. The 
draping of this garment will alone give all the 
vertical effects desired and can be made to 
expose either of the arms, either of the shoulders, 
or the whole of one side of the figure. Undoing 
one or more of the buttons or hooks allows it to 
slip from either of the shoulders, and with only 
two buttons there is a sleeveless garment. If 
all the fastenings are done up and the others 
are put close to the neck, the whole figure can 
be covered, and yet one side may be exposed at 
will. By putting a girdle or sash around the 
figure an entirely new set of folds is obtained ; 
and pulling the garment up through the girdle 
and allowing it to fall gives a characteristic and 
Diana-like effect. With a crossed girdle or 
cincture over the shoulders still another series 
of folds is obtained which confines the garment 
to the figure and shows its outlines, and one 
has at the same time the alternative of bare or 
covered arms, and one side open. Over this, 
to add to the beauty and variety of the folds, 
is sometimes put a kind of mantle, consisting of 
a piece as long as the main garment, horizont- 
ally, but only half its vertical depth. This the 
ancient Greeks buttoned on the shoulders and 
made into the same artistic folds as the under- 
garment. When the ends are cut off diagonally 
they look very well, and may be made to form 
a series of folds like pleats. Add to this a very 
long strip or scarf, about 24 in. wide and of 
indefinite length, to throw over the shoulders, 
to twist about the arms, or to festoon about the 
figure, and the photographer has all the neces- 
sary materials for the ordinary drapery of the 
full-length figure. 


DRAWINGS, COPYING 

For methods of copying drawings, see under 
the headings, ‘“‘Engravings, Copying,” ‘‘ Copy- 
ing,’ ‘‘Copying Illustrations for Translation 
into Line Drawings,’ and ‘‘ Copying Stand.” 

In process work, the copying of drawings is 


Drawings from Photographs 


brought to a high degree of perfection. Cameras, 
lenses, prisms, copying stands, arc lamps, and 
all other apparatus are specially designed for 
obtaining the most perfect negatives. Parallel- 
ism between the various parts of the camera 
and the copyboard is carefully studied. All 
possible means for overcoming vibration are 
adopted. Lenses are chosen to give extreme 
definition to the margins of the plate, as well 
as uniform illumination; and the prism or 
mirror employed for reversing must not in any 
way impair the definition of the lens, The arc 
lamps, which are generally preferred to day- 
light for commercial work, are very powerful, 
and reflectors are employed to concentrate the 
light on the copy. Care is taken to avoid reflec- 
tions from the surface. Where the copy is a 
wash drawing or painting in colours, isochro- 
matic plates and screens are employed. For 
copying bluish wash drawings, or drawings in 
which Chinese white has been used (tending to 
reproduce darker than the original), esculin or 
quinine filters are used to correct the effect of 
ultra-violet light. 


DRAWINGS MADE 
GRAPHS 

There are many methods of making line 
drawings from photographs, and most of them 
involve the destruction of the originals. In 
essence, the lines of the photograph are gone 
over with waterproof ink and the photograph 
then bleached. Matt prints on bromide, gas- 
light, or P.O.P. paper may be used, the last- 
mentioned being fixed and washed, but, if it 
can be avoided, not toned. The ink used must 
be waterproof, Indian or Chinese, applied in any 
convenient manner, as, for instance, with an 
ordinary pen, a mapping pen, a camel-hair 
pencil, etc. When sufficient work has been 
put on the print, the photographic basis is 
entirely destroyed with a powerful solvent of 
the silver image. Any reducer or bleacher may 
be used, but in practice one that acts quickly 
and without stain has its advantages, and 
therefore a mixture of iodine and potassium 
cyanide, both of which are poisonous, is the best. 
The formula is :— 


10% solution of iodine 


FROM PHOTO- 


in methylated spirit 60 drops 125 ccs, 
10 % solution of potas- 

sium cyanide in 

water . : Bra 18 ah $2 220s ss 
Water I OZ. - T0001. 5; 


This may be used stronger if the action is not 
quick enough. The solution should not be 
allowed, to touch the fingers any more than is 
unavoidable. The mixture ought to destroy 
the photograph in half a minute; the picture 
is then washed for five minutes and afterwards 
dried. 

The following process is used by many trade 
workers: Make ordinary prints on a smooth 
surface bromide paper, exposing and developing 
in the usual way; after developing, harden 
in an alum bath, wash and dry, but do not fix. 
Then draw over the picture with good water- 
proof Indian ink, and when the latter is quite 
dry bleach in a copper-bromide bath made 
by dissolving 50 grs. of potassium bromide in 


196 


Dress for Sitters 


I oz. of water, 50 grs. of copper sulphate in 
another ounce of water, and mixing the two 
solutions together. If after bleaching the draw- 
ing requires further working up, it may be well 
washed and redeveloped with any weak dry- 
plate developer, dried, worked on, and again 
bleached. After a good rinse the bleached 
image may be totally destroyed, and the lines 
left permanently black upon a white ground by 
passing the bleached print through a potassium 
cyanide or “hypo” bath. A saturated solution 
of mercuric bichloride may also be used for 
bleaching out the silver image. When the 
results are required for use as originals in line 
photo-engraving, the bleached prints should be 
kept from the light as much as possible, or 
they may turn yellow. 

A simpler process of drawing on a photographic 
base is that of using a blue (ferro-prussiate) print, 
preferably one that has not been made too dark 
by over-printing. As the light blue colour 
will not photograph, the drawing may be repro- 
duced by line photo-engraving processes without 
any bleaching, although the blue image can be 
removed, if desired, by immersing in dilute 
liquor ammoniz, by a prolonged washing in 
hard water, or better and quicker still, by 
immersing in a solution made by dissolving I 
part of potassium oxalate in 6 parts of water. 
Solutions of sodium carbonate and caustic 
potash will also bleach blue prints. 

In process work, various methods are adopted 
for making drawings from photographs. If the 
photograph is mounted, and must not be 
removed from the mount, it is best to lay over 
it a piece of tracing gelatine, scratch the out- 
line with a sharp point, and then to rub black- 
lead or red chalk into the lines. This draw- 
ing is turned face down on to a sheet of Bristol 
board, or other surface to be drawn upon, and 
rubbed down with the handle of a tooth-brush, 
or by other convenient means. The drawing 
is in this case reversed. It may be obtained 
the right way by re-scratching on the back of 
the gelatine and filling in this side instead of 
that originally traced, or it may be reversed 
by means of prisms when making the block. 

A better way is by the use of the “ Norwich 
Film,” a gelatine with a matt surface which 
can be drawn on with pencil, crayon, orink. The 
resulting drawing may be used as a photographic 
positive, or may be converted into a negative 
by flowing with a non-actinic varnish. When 
dry, the greasy ink or crayon is removed with 
benzole or other suitable solvent. 

The bleaching-out process, already described, 
is perhaps the best way of converting a photo- 
graph into a drawing. 

Unmounted prints may be traced down on 
to Bristol board or drawing paper by rubbing 
the back with blacklead or red chalk, or by 
putting common transfer paper between the 
print and the drawing surface. The outlines of 
the photograph are then gone over with a hard 
pencil or stylus. 


DRESS FOR SITTERS 

The part played by dress in photography is 
an important one; and a question put frequently 
to the photographer is: “‘ What dress shall I 
wear?” Asa general rule the more simple the 


Dress for Sitters 


dress the better if the portrait is to be what 
may be termed a lasting one. Feminine fashions 
change rapidly, and a photograph taken of a 
sitter dressed in the prevailing fashion soon 
becomes “‘ dated,” as it were. Colour is not of 
the importance it used to be, as, with the modern 
isochromatic plates and screens, fairly correct 
interpretation of tone has become possible, and 
the rendering of a yellow dress as black, or a 
blue one as white, ought now to be a thing of 
the past. W. Ingles Rogers carried out, many 
years ago, some important experiments, and the 
salient facts in his report may be summarised 
as follow: A gentleman’s ordinary dress is not 
sufficiently artistic to warrant a full-length 
presentment; its colour is preferably black. In 
the case of uniform and special dress, the full- 
length is preferable. Ladies require more careful 
treatment from the standpoint of dress. As a 
tule, long dresses make the best pictures, both 
because the length of drapery gives height and 
dignity, and because graceful and flowing lines 
are then more easily obtained. As a matter of 
fact, the female figure has no waist. It is a 
at invention, and a conventionality of form. 
f, however, such a thing has to be considered 
and sustained, the best place for confining the 
dress is just below the armpits. This disguises 
any lack of length in the lower limbs, and grace 
and dignity are gained without the usual in- 
artistic curving of the hips. 

Next to form comes colour, and in this con- 
nection no rule can be laid down that will pro- 
duce perfect results with unvarying fidelity. 
Much depends on style and complexion; but, all 
other things being equal, monochrome (black, 
white, or grey) gives the most favoured results. 
Gaudy tints are opposed to the principle on 
which the “‘science’’ of photography is based, 
and are only tolerated by the camera when 
neutralising an otherwise monotonous effect. 

In cases of necessity—for example, where the 
sitter’s wardrobe does not contain what the 
perfection of photographic art requires—the 
table of tints, with their relative photographic 


Colour of | Tint in Combines best 
Dress Photograph with 
White White Black, dark blue, red, or 
brown 
Yellow Grey Black or dark green 
Salmon: sia} 4s ae ‘ a Pe 
Pink noe ” —- %9 2° 29 
Fawn 2” Je 39 29 29 
Scarlet ..|Dark grey; White or dark blue 
Dark red .. | Black White, light green, light 
blue or grey 
Brown Black ..|White, light green, light 
. blue or grey 
Light green | Light Dark green, dark red, 
brown or black 
Light blue Ne Dark blue, dark _ red, 
or violet brown or black 
Dark green | Black Light green, yellow, or 
grey 
Dark blue|Medium |Light blue, white, or 
or mauve grey 
Grey Grey White or black 
Black Black White, light blue, green, or 


grey 


197 Dropping Bottle 


qualities, given in the preceding column, will 
repay a careful study. 

As fot materials, the following are the most 
suited to photography, arranged in the order of 
preference :— 


Name of Combines best 
Material with 
Velvet Linen, lace, crape, and fur 
Silk Crape, velvet, and fur 
Cloth Linen, lace, crape, and fur 
Serge Linen and silk 


Calico goods 
Woollen goods .. 
Fur irs wa 


Linen and cloth 
Linen and silk 
Silk, lace, and fringes 


Silver ornaments are preferable to gold, and 
if diamonds are worn they should be slightly 
smeared with soap to deaden their reflection 
during the brief period of exposure. Long, 
drooping curls or waves are effective in semi- 
ptofile, but give to the full-face sitter an effect 
of solidity. The arrangement of the hair gives 
a man his individuality in appearance, and 
therefore should not be interfered with. 


DRIFFIELD (See “ Hurter and Driffield.’’) 


DROP SHUTTER (Frt., Obturateur a guillo- 
tine; Ger., Guillotine Verschluss, Fall- 
verschluss) 

A shutter in which a panel, having a central 
opening and working in a pair of grooved upright 
rails, is caused to fall by gravity in front of 
the lens, uncovering and re-covering the latter 
as the opening passes it. This kind of shutter 
is simple and easily made, but is somewhat 
cumbrous, and will not give very rapid expo- 
sures. It has been quite superseded by the 
toller-blind shutter. 


DROPPING BOTTLE (Ft., Flacon compite- 
gouttes ; Ger., Tropfglas) 

A bottle for the delivery of a liquid or solution 

in small quantities, or in separate drops. There 


A. Dropping Bottle 
with Pipette 


B. Dropping Bottle 
with Slotted Stopper 


ate various patterns. In one, A, a pipette or 
dropping tube is let into the stopper. Another, 
B, allows the drops to pass to a suitable lip in 
the neck by turning the stopper, in which a slot 
is cut. When not in use, a second turn of the 
stopper shuts off communication with the lip. 
Schuster’s dropping bottle resembles a flask 


Dropping Tube 198 


drawn out at the top to a fine curved point, and 
having a stopper at one side for the introduction 
of the solution. 


DROPPING TUBE (Fr., Pipette 
gouttes ; Ger., Tropfrohr) 

A tube having one end drawn out to a fine 
point, and provided at the opposite end with a 
rubber bulb, as illustrated. The bulb is com- 
pressed, and the tube dipped into the liquid or 
solution to be used; on removing the pressure 
from the bulb the liquid rushes up the tube. 


compte- 


Two Patterns of Dropping Tube 


Having withdrawn the tube, the liquid may be 
delivered in drops as required by a gentle pres- 
sure on the bulb. Another form is without a 
bulb. With this, the tube is dipped into the 
solution, its upper end closed with the finger, 
and the tube withdrawn. If the depth of solu- 
tion does not allow of this, the liquid must be 
drawn up by suction with the mouth, and the 
upper end of the tube closed with the finger 
before withdrawing it from the solution, but 
this is very inefficient. On removing the finger 
the liquid is delivered in drops. It is risky to 
use this kind with poisons, lest the solution 
should reach the mouth. A fountain-pen filler 
is an excellent dropping-tube for quite small 
quantities, 


DROPS (Fr., Gouttes ; Ger., Tropfen) 

Drops and minims are supposed to be syno- 
nymous, but such is not the case. A minim is 
one-sixtieth part of a dram, but a drop may 
measute more than a minim, or less, as shown 
by the following list, which gives the average 
number of drops which go to make up one 
dram: Water, 71; nitric acid, 96; hydro- 
chloric acid, 70; sulphuric acid, 100; ether, 
290; alcohol, 130; turpentine, 220; castor 
oil, 157; olive oil, 168. Drops also vary accord- 
ing to the way they are dropped and the recep- 
tacle they are dropped from, but happily in 
most photographic operations extreme accuracy 
as to the size of adrop does not matter. A useful 
atrangement in the form of a squirt, and called 
a minim-meter, is sold by most chemists for the 
purpose of measuring drops, or, more correctly 
speaking, minims. 


DRUMMOND LIGHT 


An early name for the limelight, which is 
described under its own heading. 


DRY COLLODION 

This term is sometimes applied to collodion 
emulsion which has been precipitated and washed 
with water, and occurs in the form of fine flocks 
or granular masses, which only require solution 
in alcohol and ether to form a normal collodion 
emulsion. (See also ‘ Collodion.’’) 


Dry Mounting 


DRY COLLODION PROCESS 

An old process, not now used, in which plates 
were coated with an iodised collodion, sensitised 
in a silver bath, washed, and bathed in certain 
so-called preservative solutions, such as albumen, 
honey, beer, tannin, coffee, laudanum, etc., 
most of which were hygroscopic to some small 
extent, and thus kept the film slightly damp. 
The first of the dry collodion plate processes of 
any real service was that published by Dr. J. M. 
Taupenot, on September 8, 1855. The original 
method was to pour over the collodionised and 
sensitised plate a solution of iodised albumen, 
dry, and dip for a second time into a silver 
hitrate bath, wash, and dry. Plates prepared in 
this way kept good for six or eight weeks. 
Mayall suggested a similar process in May of the 
same year. The great drawback of the process 
was its slowness, the plates needing about five 
times the exposure of wet plates. On May 21, 
1855, Dr. Hill Norris, of Birmingham, published 
his famous process, Fothergill following with his 
ptocess in 1856. Dry collodion plates then be- 
came articles of commerce, the Hill Norris 
collodio-gelatine plate (patented September 1, 
1856) becoming the most popular, 


DRY ENAMEL PROCESS 

A method used in printing the half-tone image 
on to zinc or copper for etching. The sensitive 
solution consists of— 


Ammonium bichromate 125 grs. 25 g. 
Powdered white sugar 270 ,, ee 
Chromic acid . + ROS Diy £655, 
Albumen, from 2 eggs 7 eggs 
Liquor ammonice . 120 mins. 24 CCS. 
Water 10 Oz, 1,000 7.3; 
An alternative formula is— 

Grape sugar . 232 Sts. ic Faerie, 
Albumen : . 338 Inims, aoe, 
Ammonium bichromate 46 grs. es ap 
Chromic acid Est epee ue 
Liquor ammonize . 120 mins, 24 ccs 
Distilled water 4} 0z. 1,000 ,, 


After coating the plate with this solution and 
printing, it is dusted with finely powdered 
anhydrous sodium carbonate, or magnesium 
carbonate, brushing with a soft flat brush until 
the image is clearly visible. A small room, in 
which the atmosphere can be kept moist by 
standing a bowl of water on the floor, is neces- 
sary, so that the plate can absorb the requisite 
amount of moisture to attract the powder. The 
plate is burnt in, as usual in the enamel process, 
and then placed in water, when all the parts 
which have absorbed the powder develop away 
quite clean. If any scum remains, a little moist 
salt or dilute caustic potash will remove it. 


DRY MOUNTING 

The Derepas is perhaps the most perfect 
method known of mounting prints and of building 
up multiple mounts. The surface of the print is 
not affected; there is nothing that will harm 
the most delicate print by any process; there 
is no cockling, even when a stout print is mounted 
on a thin paper ; and it is durable when properly 
carried out. A sheet of thin tissue is prepared 
with shellac, the prepared tissue being com- 
mercially obtainable. A piece of the tissue is 


Dry Plates 


touched with a hot iron, which will make it 
adhere to the back of the print, and both print 
and tissue are then trimmed together. They are 
next placed in position on the mount, covered 
with a sheet of paper, and subjected to heat. 
This is accomplished either by going over it 
with a hot flat-iron, or subjecting it to pressure 
in a heated press made for the purpose. The 
heat causes the shellac to melt and so secure 
perfect adhesion between print and mount. 
Everything being dry there is no expansion with 
its subsequent contraction, and print and mount 
remain smooth and flat. There are no special 
difficulties attached to this method, and the 
results are excellent. 


DRY PLATES (Fr., 
Trockenplatten) 
Sheets of glass of given sizes coated with gela- 
tine emulsions. The term arose in the early 
days to differentiate them from wet collodion 
plates. The introduction of the gelatine dry 
plate marked a new epoch in photography. 
There is some difference of opinion as to who 
was the actual inveutor, Burgess, Maddox, 
Kennett, Wratten, and others all working at the 
same time in practically the same direction. It 
was, however, on September 8, 1871, when 
Dr. Maddox published an account of his experi- 
ments, that the first hint was given. On July 
18, 1873, J. Burgess, of Peckham, advertised 
and sold ready-made emulsion with which 
photographers could coat glass and so make their 
own dry plates; Kennett followed, and on 
November 20 of the same year took out a 
patent for his “ pellicle,’ with which photo- 
gtaphers could make their own plates. Improve- 
ments followed rapidly, Bolton, Sayce, Wratten, 
Mawdsley, Berkeley, Abney, Bennett, and 
others doing much to bring the dry plate to per- 
fection and to make it an article of commerce. 
As far as can be ascertained, the first ready-made 
dry plates were advertised in April, 1878, by 
Wratten and Wainwright and the Liverpool 
Dry-plate Company (Peter Mawdsley), the plates 
by the latter firm being called the “ Bennett 
Plates,’ and the price for quarter-plates being 
3s. per dozen. It was not until 1880 that gela- 
tine dry plates became really popular. 

In process work, considerable progress has 
been made of late years in the use of dry plates. 
Excellent commercial dry plates, specially made 
for line, half-tone, or colour work, are now 
obtainable. The methods of handling are not 
very different from those in ordinary photo- 
graphic work, except that greater care has to 
be taken to avoid over- or under-exposure and 
fog; the lines must be kept perfectly clear and 
sharp, and in half-tone work great care and skill 
have to be exercised to obtain sharp dense dots 
of the right size and quality. In this respect 
dry plates are more difficult to handle than wet 
collodion. Backing is found to be an advan- 
tage; the negatives usually have to be cleared 
with ferricyanide and “ hypo” (Howard Farmer’s 
reducer); and intensification, preferably with 
silver cyanide, is generally necessary. For the 
making of dry plates, see ‘Coating,’ ‘‘ Kmul- 
sion,” etc. For the various manipulations, see 
“‘Exposure,” “Developing,” “Fixing,” ‘“ Ton- 
ing,” “Washing,” etc. 


Plaques séches; Gert., 


199 


‘Drying Box or Cupboard 


DRYING BOX OR CUPBOARD (Fr., Etwve, 
Armoire ; Get., Trockenofen) 

A light-tight box or cupboard used in drying 
gelatine plates after coating, and for other photo- 
graphic purposes. ‘The chief requirement is the 
circulation of a current of dry air, in order that 
the internal air may be continuously drawn away, 
catrying with it by degrees the moisture from the 
plates. The temperature of the drying cupboard 
requires to be raised, but perfect ventilation is 
of greater importance. A pattern recommended 
by W. K. Burton consists of a box with a closely- 
fitting light-tight door, and having light-trapped 
air openings at top and bottom. Beginning near 
the bottom, a bent channel or flue runs up 
against one side of the box, a gas burner being 
inserted in it near the top. When the burner 
is lit it draws a current of air through the flue 
from below, and consequently ensures a con- 
stant circulation of air in the box. Another 
kind of drying cupboard is warmed from beneath 
by a gas-ring or oil stove, a sheet-iron bottom 
being fitted. Light-trapped openings at the 
lower portion of the sides and a _ cowled 
ventilator at top furnish the necessary air 
current. 

In process work, the arrangement for drying 
collotype plates is usually in the form of a box 
or trunk supported about 12 in. from the 
floor on four legs. The bottom consists of an 
inverted sheet-iron box, under which is placed 
a gas-ring or pipes. Holes are punched in the 
side of the box to prevent the gas becoming 
choked. The wooden part of the box is about 
18 in. deep. About 6 in. from the top are two 
iron bars, resting on ledges at the sides of the 
box. These bars are provided with screws 
placed at suitable distances with their points 
upwards. ‘The plates rest on these screws, and 
by adjustment of the latter can be levelled up, 
so that the gelatine solution on the plates will 
not run off. The bottom of the box is usually 
covered with sand to equalise the heat. The 
lid of the box is covered with gauze or an open- 
textured cloth, so that the moist air can pass 
through. A thermometer is inserted into the 
box through a hole in the lid. 

Process workers find a drying cupboard 
necessary for quite a number of purposes; in one 
convenient form the bottom takes the form of 
an inverted sheet-iron box, and there are holes 
in the sides to allow the gas fumes to escape, or 
a flue pipe can be led out from the back. In 
the sides of the wooden part, just above the 
sheet-iron bottom, are holes for drawing in a 
cutrent of air; these holes are covered with a 
baffle-board sloping towards the bottom. Shelves 
or racks can be placed in the cupboard. On 
the top a metal cowl ventilator is placed. For 
heating, an ordinary gas-ring burner is placed 
underneath the bottom. The cupboard can be 
elaborated by placing an electric radiator inside 
and an electric fan on top to draw out the air. 
The incoming-air can also be made to pass 
through an opening packed with damp cotton- 
wool, so as to stop any dust entering. For 
colour-sensitising dry plates the cupboard must, 
of course, be made perfectly light-tight. Such 
a cupboard is very convenient for drying photo- 
lithographic paper and carbon tissue, and will 
be found generally useful. 


Drying Marks 200 


DRYING MARKS 

These in negatives are most frequently patches 
or portions which are stronger or weaker than 
the remainder of the image, such portions pro- 
ducing corresponding defects in the print. These 
markings may be due to defective working, or 
to causes beyond the worker’s control. With 
regard to the first, a plate may be drying very 
slowly, and when partly dry the conditions of 
drying may be changed to accelerate the drying 
of those parts that still remain wet. The part 
accelerated will almost always show greater 
density than the remainder, and at times a 
well-defined mark may separate the two 
parts. 

The second cause is uneven drying of the 
plate in the course of manufacture. When plates 
are racked for drying, no matter how perfect the 
ventilation of the drying-room may be, the 
edges, where the emulsion always tends to thin- 
ness of coating, will always dry more quickly 
than the centre, the result being that a line 
appears round the edges. The exact cause of 
this is a little obscure, but the most satisfactory 
explanation is that given by Homolka, who 
ascribes the foggy line—for this is what edge 
drying marks actually are—to a diffusion of the 
faint traces of soluble haloid left in the emulsion 
from the thin dry edge to the thicker and moister 
centre. Actual drying marks from uneven dry- 
ing of plates during the manufacture are now 
rarely met with, though in the early days of dry- 
plate photography they were of frequent occur- 
rence, and manifested themselves in precisely the 
samme manner as in the unequal drying of nega- 
tives—that is, by central patches of greater or 
less density due to this portion being more or 
less sensitive than the margins. 


DRYING NEGATIVES 

Negatives should be dried as quickly as possi- 
ble consistent with drying eyvenly—that is, 
with uniformity in the rate of drying. A 
current of dry air is best, but a drying cupboard 
is good. In any case, the air should have free 
and uniform access to their surfaces ; they should 
not be dried close together, as in a draining rack, 
neither should they lean against a wall face 
downwards. The place chosen should be as free 
from dust as possible, and not too warm, or the 
gelatine may melt. In summer and autumn 
particuarly, it is necessary that the plates should 
be dried in a place protected against flies and 
other insects. Cockroaches are said to be fond 
of eating wet gelatine. 


DRYING PRINTS 

Prints in all processes should be freely exposed 
to the air in drying, so that the operation may 
be rapid. The most satisfactory method in 
most cases is to hang the prints from a line or a 
lath, either by means of clips or by pins through 
one or two corners. An alternative method is to 
blot off as niuch moisture as possible, either with 
a soit towel or blotting-paper, and then lay the 
prints face upwards on a clean white cloth until 
dry. <A drying cupboard is the best place for 
the latter method. In any case, they should be 
dried in a place as free from dust as possible. 
(For imparting a high gloss to prints in drying, 
see “ Glossy Surfaces.”’) 


Dufay Dioptichrome Process 


DRYING RACK, OR DRAINING RACK 
(Fr., Séchoir, Egouttoir : Ger., Trocken- 
gestell) 

A wooden, metal, or porcelain stand with 
grooves, in which negatives, etc., are stood up 
to drain and dry after washing. The ordinary 
wooden folding pattern is shown at A, while B 


A. Wooden Drying Rack 


illustrates an ingenious expanding metal tack, 
which may be adjusted to hold various sizes 
of plates. Many washing tanks are fitted with 
a femovable metal rack which may be used for 
drying. Negatives should not be placed closely 
together in the racks when drying, or the process 


%, 
i Vestzs 
oe 


a eens Veh 
sega aas SRNL 
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is 

) 

Su 
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- 
= 
SS 


B, Expanding Metal Drying Rack 


will be very slow, and uneven patches sometimes 
occur. The closeness of the usual grooves is in 
this respect somewhat misleading. It is better 
to spread out the negatives, 


DUFAY DIOPTICHROME PROCESS 

This employs a screen plate of French manu- 
facture. A gelatinised glass is coated as to two- 
thirds of its surface with a greasy material, which 
acts as a temporary resist, in the form of lines, 
points, or grains of geometric or irregular shape. 
The present plate consists of lines with rectangles 
in between. The bare parts are dyed and the 
whole surface varnished and treated with a 
solvent of the greasy material so as to lay bare 
the unstained gelatine. Half this surface is 
then again covered with a greasy substance, and 
the bare gelatine again dyed, again varnished, 
the greasy material again dissolved, and the 
last portion of the unstained gelatine dyed. A 
compensating filter is used, and the plate is 
issued with a special panchromatic plate fitting 
into a frame with nickel pins which allow of 
complete registration of the positive and colour 
screen, Coloured plates to this work show the 
formation of the Dufay plate, and a typical result 
obtained with this plate. 


Du Hauron, Ducos 


- The plates must be manipulated in absolute 
darkness or with the maker’s special dark-room 


filter. The developer recommended is :— 
Metol i , $F-Rre. 6 g. 
Sodium sulphite . EOE, rip es 
Hydroquinone 17 gts. - 3 
Potassium bromide fi Sane age 
Liquor ammonie (°880). 130 mins. I5 ccs. 
Distilled water to 20°02.) F000, 


For use, mix with an equal quantity of water 
and continue development for four minutes. 

Rinse the plate for some minutes, and immerse 
in— 

Potassium or ammo- 


nium bichromate 44 ers. 5. @. 
Sulphuric acid . - 95 mins. IO ccs. 
Water to. ‘ 20 OZ. TOO. ys 


When the image has dissolved, wash for 
several minutes till all the yellow tint has dis- 
appeared, and immerse in the first developer or 
preferably in— 


Metol ; : 22 gts. 2*hon8 
Sodium sulphite I OZ. BO 55 
Hydroquinone . 44 gts. ae 
Potassium carbonate 220 ,, \ epee 


Potassium bromide . 18 ,, Bye 
Distilled water to 1,000 ccs. 
Re-development takes about three minutes, and 
should be done in a bright light. The plate 
may be reduced with “hypo” and ferricyanide, 
and intensified with mercuric chloride followed 

by ammonia. 


DU HAURON, DUCOS 

A Frenchman, born in 1839, in Langon, 
Gironde, and one of the first to describe in detail 
the three-colour process (1867). In 1864 he 
patented a species of kinematograph. He was 
also the inventor of the anaglyph, and the first 
to describe a screen-plate process of colour 
photography. 


DUOTYPE (Ger., Duplex-Autotypie) 

A half-tone in two printings, one being with 
a light tint ink, and the other in a black or photo- 
brown, the idea being to imitate the tones of 
a photograph. Sometimes both printings are 
from the same block, but the best results are 
obtained from two blacks etched differently. 


DUROLENE 

A kind of unbreakable glass in which wire is 
embedded. It has been recommended for studio 
roofs, but its tint stops a large amount of actinic 
light. 


DUST PREVENTION 

Dust is often a great trouble in photographic 
work, both in the field and in the work-room. 
Dust in the camera and on the lens is the most 
frequent cause of trouble, hand cameras being 
more prone to the defect than others because of 
the usual practice of carrying them unprotected. 
Dusty lenses cause flat and misty pictures. Dust 
will find its way into the lens through the slits 
used for Waterhouse and rotating diaphragms, 
and the only preventive is to fit, when possible, 
a band of velvet ribbon round the lens tube 
to cover up the slots as much as possible; in 
the case of Waterhouse diaphragms the band 


, 

oo ee t 
ae | 
- - 


201 


Dust Spots 


may be kept completely over the slot when the 
diaphragm is not in use. Rubber bands have 
been recommended, but these contain substances 
that tend to mark and discolour the lens mounts. 
The plate-changing arrangements in hand 
cameras, and shutters working inside, are often 
the means of stirring up dust which settles upon 
the lens and plate. Frequent dusting of the in- 
terior of the camera and plate sheaths is advis- 
able, but unless done carefully more dust will be 
deposited than removed. Coating the inner- 
most parts of the camera with glycerine or vase- 
line has been suggested; such a coating will 
naturally hold down the dust and prevent its 
flying about, but inasmuch as it is liable to be- 
come messy and to need frequent changing, the 
method is not recommended. The focusing 
screens of stand cameras are occasionally thinly 
coated with vaseline in order to make them more 
transparent, and the coat serves as a kind of trap 
for the dust; in this case the cleaning is quite 
easy, but the cleaning of the interior of the 
bellows is quite another matter. Dark-slides 
invariably attract dust, but they can easily be 
dusted, and any coating of grease might inter- 
fere with the sliding shutter or find its way to 
the plate. Dark-slides having draw-out shutters 
are the greatest offenders; the light-trap at the 
top of the slide, which closes the aperture when 
the shutter is completely withdrawn, is made 
usually of either velvet or rubber, and this 
Scfapes or wipes the dust from the sides of the 
shutter as it is drawn out and returned, thus 
in time forming an accumulation. Thorough 
dusting of the light trap and the interior of the 
slides is an obvious remedy. Dust settling upon 
the plate causes many spots, and it is of but 
little use dusting a plate before putting it into 
the dark-slide if it is to be exposed to a minia- 
ture dust storm in the camera. 

Plate dusters are articles of commerce, but 
if they are not kept scrupulously clean they put 
more dust upon the plates than they take off 
and do more harm than good. Plates rarely 
need dusting with a brush; when taking them 
from the box or dark-slide, a gentle knock with 
the edge upon a table will do all that is neces- 
sary. Of dusters, an old well-washed silk hand- 
kerchief is one of the best. 

Frequently unsuspected resting-places for dust 
are the top rims of bottles and the crevice 
between the cork and the bottle neck; before 
pouring a developer from a bottle, the rim and 
mouth should be wiped, otherwise any accumu- 
lated dust may find its way to the plate and 
cause spots. The corks of bottles should be 
kept covered with a paper or cardboard cap. 

Many professional dark-rooms and all plate- 
making rooms have their floors kept damp in 
order to prevent dust. 

The utmost care is necessary when mixing 
chemicals, more particularly pyro and other 
developers, to prevent small particles of the 
developer in the form of dust flying about the 
room and settling upon sensitive surfaces. 


DUST SPOTS 

Miniature transparent spots on negatives due 
chiefly to the causes given in the preceding 
atticle. If the spots are actual holes in the 
gelatine, showing the bare glass beneath, they 


Duster, Plate 


are due to dust in the process of manufacture 
and are real pinholes; but these are very rarely 
met with nowadays. Dust spots are more or 
less numerous and of various shapes and sizes, 
and they occur where dust specks have rested 
on the plate during either exposure or develop- 
ment. In the former case they prevent the 
light from reaching the emulsion, and in the 
latter the developer is prevented from reaching 
it. The remedy for spots caused in this way 
(it is a mistake to call them “ pinholes’’) is 
careful spotting, but obviously prevention is 
better than cure. Particles of developer dust 
which may float about the dark-room and settle 
upon undeveloped plates and bromide papers 
invariably cause black spots, but such spots 
will also appear when the developer has not 
been properly dissolved, and it is very difficult 
at times to discover the real cause of the trouble. 
Black spots on a negative are best left alone, 
and the resultant white spots on the print 
touched out. Etching or pricking away with a 
needle on the negative has been recommended, 
but it needs particular care, as otherwise the 
film will be ruined. 


DUSTER, PLATE (Fr., Torchon aux plaques ; 
Ger., Plattenabstaiber) 

A strip of wood having a piece of plush 
attached, and used for dusting dry plates before 
insertion in the dark-slide. Sometimes a wide 
camel-hair brush is employed, but this is still 
less satisfactory, being more liable to put dust 
on the plate than to remove it. Neither device 
is recommended. (See also “‘ Dust Prevention.’’) 


DUSTING OR GRAINING IN PROCESS 
WORK 1 (Fr., Grainage; Ger., Staub- 
kornung) 

There are several processes of photo-engraving 
dependent on the laying of a ground consisting 
of fine resin, bitumen, or other similar material. 
Such a method is used for aquatint etching 
instead of the old way of flowing on the resin 
emulsified in alcohol. 

For a process of colour work much practised 
in France, called chromo-typogravure, a resin 
grain is laid on zinc plates, and a set-off is laid 
down on the plates from a key plate to guide 
the etcher in stopping out the various colours. 
This is done by means of an acid-resisting varnish, 
so that the resin ground forms the lighter tints. 

In the photogravure process the laying of 
the ground is an important operation. Finely 
powdered bitumen is generally used, and after 
being deposited on the copper plate and fixed 
by heat, a carbon print is developed upon it to 
form the resist for etching. 

The dusting for the foregoing processes is done 
by means of a dusting box. This may be of 
either the turnover pattern or the fan pattern, 
the former being suitable for small plates and 
mostly used by amateurs. The box is turned 
over and over to shake up the bitumen, then 
the plate is put in and the box allowed to stand 
for a shorter or longer time, as may be demanded 
by the character of the grain required. In the 
fan dusting box the powder is stirred up in the 
semicircular zinc bottom by means of a revolving 
brush, and, after allowing to stand for a few 
moments for the heavier particles to settle, the 


202 


Dusting-on (Powder) Process 


plate is put in. The longer it remains in the 
box the finer will be the grain. Powdered lac 
is also sometimes used for dusting. 


DUSTING-ON (POWDER) PROCESS (Fr., 
Procédé aux poudres ; Ger., Einstaubver- 
fahrung) 

Known also as the ‘“‘ Powder Process,” based, 
as are the other carbon processes, upon the 
oxidising action of chromic salts upon organic 
matters. In the present instance, the organic 
matter loses its tackiness or stickiness under 
the action of light and refuses to retain dust. 
The process is largely used in the production 
of photo-ceramics and for the intensification and 
doctoring of faulty negatives when these are of 
great value. Various substances are available 
for the support of the powder picture, but none 
is better than ground opal or pot opal glass. 
As the effect of the light in the process is to 
cause the film to refuse to take powder, the parts 
acted upon remain light; this being the case, 
a transparency (positive) must be used for 
printing from and not a negative, as a print 
trom the latter in this process would be a nega- 
tive. The requisites are sensitising mixture, 
opals, powder, and a transparency of excellent 
quality. Although opal has been named and 
is recommended, glass, ferrotype, and other 
supports can be used. In any case, it must 
provide a proper contrast to the powder. Thus, 
if the dust or powder used is silver or gold 
bronze, the image may be produced on a dark 
background, for which a ferrotype tinplate will 
serve. 

The support must be cleaned and sensitised 
in a solution consisting of a gum, a hygroscopic 
substance, and a light-sensitive medium. The 
following formula is one of a great number 
between which there is but little to choose :— 


White sugar . 200 grs. 20 gy 
Gum arabic REO Ge. 25°35 
Ammonium bichromate 200 ,, 20): 
Methylated spirit 1 Oz.” 50 ccs 
Water : 20°° 5 T0002 35 


An old, and possibly the original, formula, still 
in use, is as follows :— 


Water : A IO Oz. 1,000 ccs. 
Dextrine . . - 240 gts. 48 g. 
Grape sugar » RAD 48 ,, 
Potassium bichromate 240 ,, aay 


The first of these formule is said to possess 
many advantages. The gum and sugar should 
be covered by the water and dissolved by heat ; 
when cool, the other ingredients are added. The 
spirit is used simply to make the solution flow 
over the plate more evenly, and more or less 
may be used as desired. After washing, the 
wet plate is flowed over with the sensitive mix- 
ture, drained for a few minutes, and then baked 
in an oven until bone dry. The operations up 
to baking may be carried on in daylight, but as 
the plate dries it becomes sensitive and should 
therefore be removed and examined in a dull 
light. The plate is then ready for exposure 
under a positive, and, as in many other cases, 
this is the most difficult part of the process, for 
so much depends upon atmospheric conditions. 

The duration of exposure can be found only 
by experiment, but as a rough guide it may be 


Dusting-on (Powder) Process 


said to be one minute in bright sunlight on a 
summer’s day, when a transparency of average 
density is used. When exposure is complete, 
the plate is “‘developed’”’ by dusting on a 
powder. The choice of a powder is almost 
unlimited, but it must be exceptionally fine, to 
ensure which it should be sifted through a muslin 
bag. Ordinary powder colours from an oil-shop 
may be used. Ivory black and Indian red are 
good colours, used alone or mixed in varying 
proportions, while some use levigated graphite. 

For printing, the sensitive plate should be 
warmed, or it may be warmed by being printed 
in strong sunlight. An image will be seen 
faintly upon the sensitive plate when removed 
from the frame. The plate is held in the fingers 
or on a pneumatic holder, and some powder 
sprinkled over the surface, immediately spread 
with a soft camel-hair brush, and kept on the 
move until sufficient detail and density have 
been secured. 

Development proceeds rapidly as the plate 
cools, and it should be assisted by a gentle 
stream of air blown from the mouth across the 
plate, the current not being strong enough to dis- 
turb the powder or cause excessive moisture ; the 
air must not be absolutely dry, and the powder 
must be kept on the move with the soft camel- 
hair brush. Almost any depth can be obtained 
in any part of the picture by patient re-applica- 
tion of the powder rather than by attempting 
to make too much powder adhere at one time. 
As the progress of development is visible and 
under perfect control, it is not difficult to bring 
out or keep back certain parts, and in this way 
very artistic results may often be easily obtained. 

When development is complete, the powder 
picture may be coated with plain collodion and 
washed free from greasiness; the plate is now 
transferred to a 5 per cent. solution of potash 
alum until the yellow bichromate salt has been 
removed. Fixing with collodion as just described 
may be dispensed with when a duplicate negative 
is being made upon glass, all that is necessary 
being to expose it again to the light to get rid 
of all further tackiness. When, however, it is 
desired to fix the picture—as, for example, when 
it is upon an opal base—and it is not convenient 
to use the collodion “‘ fixer,’’ the picture may be 
washed over with the following solution :— 


Water ‘ FeQZ, 100 ccs. 
_ Sulphuric acid . eo Oenis, DS ene 
Methylated spirit . 2 oz. BO 


Mix in the order given. The plate is treated 
with this until all the yellowness has gone, is 
then washed gently in water, and dried by 
gentle heat. The collodion fixer is preferable, 
as with the acid solution there is a risk of 
entirely losing the image. Flatness in a picture 
is caused by over-heating or over-exposing the 
plate or by developing in too dry an atmosphere ; 
in this connection care must be taken to keep 
white light from the image before fixing. 

This process has been used for the production 
of pictures in colour. In 1888 a process was 
introduced by Germeuil-Bonnaud which con- 
sisted in exposing a plate coated with treacle, 
sodium borate and potassium bichromate, under 
an ordinary positive transparency. It was then 
dusted with various coloured pigments which, 


203 


Dyes as Colour Sensitisers 


it was claimed, adhered selectively to the differ- 
ent parts of the picture, a claim that has not 
been substantiated. Dr. Miethe has worked out 
a variation of the idea. Glass plates are coated 
with the following mixture :— 


Gelatine 9 grs. 5°8 g 
Sugar candy Sek 6 bee 194 ,, 
Potassium bichromate go ,, a 
Water 34% OZ. 1,000 ccs. 


The plates are dried in an oven and exposed 
under a positive while warm. Three prints will 
be required from three negatives representing 
the three different colour sensations. Develop- 
ment is performed by brushing on the plates 
suitable transparent powder colours. The yellow 
print is made first, stripped with collodion, and 
affixed to a card with gelatine solution. When 
dry, this is coated with a thin film of shellac, 
and the red and the blue prints superimposed 
upon it in the same manner, 

A formula specially compounded for ceramic 
work, but which will also serve for all papers 
and articles, is :— 


Gumming Mixture 


A, Fish-glue I OZ. I0O ccs, 
Glucose eee Aes 250 g. 
Glycerine . 10 drops *5 «ccs. 
Water iO 07. ¥,000-=",; 

Sensitising Mixture 

B. Am. bichromate . I oz. 100 g. 

Water ; ee I,000 ccs. 


9 
Mix together equal parts, and use as already 
described. 


DYES AS COLOUR SENSITISERS 

The peculiar property possessed by certain 
dyes of conferring upon the silver halides in- 
creased colour sensitiveness was discovered by 
Vogel in 1873, has had a most important influ- 
ence on the advancement of photography in 
almost every branch, and since his time the 
number of dyes which act as sensitisers has 
been and is being continually increased, though 
the practically valuable ones are but few. It’ 
was but natural to expect that an examination 
of the chemical constitution of the various 
sensitisers would show some common property 
or grouping of elements to which might be 
ascribed the sensitising power, but up to the 
present no definite conclusion can be come to. 
It has been further suggested that the sensitive- 
ness of the sensitisers themselves to light was 
the cause of their action, but some of the most 
fugitive dyes are not sensitisers, whilst others 
which are very stable are. Then, again, it has 
been pointed out that many of the dyes are 
photo-electric, and that here electrons may be 
set free which act on the silver halide, causing 
increased ionisation of that part of the silver 
halide which forms the latent image. The sub- 
ject is so complicated, and the mass of material 
available for examination is so meagre, that 
the resulting definite conclusions are disappoint- 
ingly small. 

There are certain generally accepted facts 
as to sensitisers, and these have been most con- 
cisely summarised by Eder as follows :—(1) The 
absorption spectrum of neither the alcoholic 
nor of the aqueous solution of the dye nor of 


Dyes as Colour Sensitisers 


the dyed gelatine agrees with the position of 
maximum action on the sensitive emulsion. 
(2) The position of maximum action of the dyed 
silver bromide always lies slightly nearer the 
red than the absorption maximum of any solu- 
tion of the dye. (3) The position of maximum 
of absorption of the dye in gelatine and the 
maximum sensitising action generally differ by 
about 30 w wu or wave-lengths. (4) The absorp- 
tion spectrum of a dyed silver halide coincides 
with the maximum sensitising action. (5) The 
dye must stain the silver halide itself to be a 
sensitiser, but all dyes that thus stain are not 
sensitisers. (6) Fluorescence, or fugitiveness to 
light, of the dye appears to play no part. 

As most of the important sensitisers are briefly 
described under their respective names, refer- 
ence should be made to these. The principal azo 
sensitisers are glycine red, benzonitrol brown, 
Pluto black, dianil black R, and wool black 4 B. 
To the rosaniline family belong ethyl violet and 
formyl violet. The phthaleine group is one of 
the most important, as it comprises the eosines 
and erythrosine. The acridine dyes are chrys- 
aniline, acridine yellow, and acridine orange. 
The best sensitisers, particularly for red, belong 
to the chinoline or quinoline group, and are 
isochinoline red, dicyanine, and the isocyanines 


204 Dynactinometer 


orthochrom T, pinaverdol, pinachrome, homocol, 
isocol, etc, . 


DYES FOR COLOURING PHOTOGRAPHS 

In choosing dyes for colouring photographs 
on a gelatine basis it is important to take into 
consideration first their stability when exposed 
to light, and secondly their affinity to gelatine. 
The following are the most suitable: acid violet 
7 BN, wool blue N extra, patent blue, fast acid 
violet, acid green, alizarine cyanine (blue violet), 
tartrazine (yellow), chinoline yellow, brilliant 
orange, Ponceau 5R (red with violet tinge), 
new coccine (bright red), erythrosine (bluish red), 
fast brown, water soluble fast blue and water 
soluble nigrosine (blue black). All these cotours 
will take well on gelatine if it has not been 
hardened. For collodion prints it is advisable 
to use albumen as a vehicle for the dyes. 


DYES, IMPROVING NEGATIVES WITH 
(See “ Retouching, Chemical.’’) 


DYNACTINOMETER _ (Fr., Dynactinométre ; 
Ger., Dynaktinomeier) 
An instrument by which the actinic power of 
light may be measured, or the rapidity of differ- 
ent lenses compared. 


ee 


Te 
pT: 


EASEL, ENLARGING (Fr., Chevalet @agran- 
dissement, Chevalet ad reproduction ; Ger., 
Vergrésserungs-Stativ) 

A support to hold the bromide paper during 
the operation of enlarging. In order to ensure 
parallelism with the negative in the enlarging 
camera or lantern, the easel is made to run on 
tails; or it is fixed, the lantern or camera being 
moved instead. The easel may consist simply 


ry BA! i i 


—— 


A, Typical Modern Enlarging Easel 


of an upright board supported by a firm base or 
crosspieces, but it is a great convenience if it 
possesses a swing movement, which will permit 
the correction of vertical lines that are shown 
as slanting in the negative, through the tilting 
of the camera when taken. Formerly the worker 
was content to fasten up the bromide paper with 
pins ; now many easels are provided with spring 
clamping bars, which save time and also hold the 
paper flatter. Another arrangement is to attach 


B, Enlarging Easel which Readily Assumes 
Horizontal Position 


to the easel a hinged frame carrying a sheet of 
glass, this being fastened down over the paper. 
A illustrates a typical modern enlarging easel, 
with rising, falling, and swing movements; 
while B shows an easel of very solid construction, 
which, besides allowing for rise and fall and for 
any degree of swing, may instantly be changed 
to a horizontal position for pinning the paper, and 


E 


as easily returned to its former upright position, 
in which it automatically catches. Some easels are 
made with a ground-glass focusing screen, so that 
the projected image may be focused from the 
back; these may, or may not, be provided also 
with a dark-slide to carry the paper. The easel 
is preferably painted black; otherwise, when 
only a part of the negative is to be enlarged, a 
good deal of stray light will be reflected from the 
easel. The white paper used to focus on should 
preferably be removed, or covered with some- 
thing black, before fastening up the bromide 
paper. In the majority of cases, however, this 
may be omitted without any ill result; but it 
is imperative if plates are used, as when making 
enlarged negatives, etc. 

It is sometimes necessary in enlarging to 
correct the distortion in the original negative 
by swinging the easel out of parallelism. In 
a typical easel for process work, both a ver- 
tical and horizontal swing can be obtained, 
and the negative can also be turned in its own 
plane to any axis. Max Jaffé, of Vienna, has 
done some remarkable panoramic copying with 
an easel of this kind, securing pictures with an 
enormously wide angle by ignoring the original 
distortion in the negative and correcting it when 
copying, at the same time joining up the image 
on one negative to another to secure a large 
combination negative. 


EAU BROME 

Bromine water; used at one time in the 
daguerreotype process, for stopping the action 
of light. 


EAU DE JAVELLE (Fr., Eau de Javelle ; 
Ger., Bleichwasser, Javellische Lang) 

A clear, colourless fluid smelling of chlorine, 
used as a reducer, ‘“‘ hypo” eliminator, and stain 
remover ; known also as sodium hypochlorite, 
ozone bleach, and Labarraque’s solution. It was 
one of the earliest of the bleaching solutions, 
and was first made at Javelle, Paris; hence its 
name. There are several methods of making 
it, the best for photographic purposes being : 
Add 1 oz. of sodium carbonate to 4 oz. of water, 
shake well, and add 320 gers. of bleaching powder 
(chloride of lime), and shake well again. Filter, 
shake up the residue with water, and again 
filter. The filtrate is a solution of hypochlorite 
(eau de Javelle). Acidified with oxalic acid, it 
forms an active stain remover, but it is safer 
to use it without the acid. Its use is not now 
recommended, safer methods having super- 
seded it. 


EBONITE 

A black compound of indiarubber or caout- 
chouc, sulphur, and pigment, with occasionally 
certain filling substances, used for the shutters 


205 


Ebony Stain 206 Eclipses, Photographing 

of dark slides, developing dishes, etc. It is the Gelatine : ; Boe 500 g 

same as vulcanite except that the latter is made Glycerine : F $,, SO 

in many different colours. Zinc oxide . ; eat TO 
Ebonite has many uses in photography owing Water . IO Oz, 1,000 ccs. 


to its waterproof and acid-proof character. Its 
drawback, however, is its brittleness, though 
this can be overcome, and a flexible ebonite 
obtained, which is useful for some purposes. 
Ebonite has been used for dipping baths for 
wet collodion work, but has not proved popular 
because of a supposed tendency for the bath to 
be injuriously affected. More probably this is 
due to the difficulty experienced in cleaning 
such baths. 

Eybonite dippers for the silver bath, however, 
survive, and have the advantage of not being 
so fragile as glass. Ebonite plate lifters for 
flat dishes and trays are also largely used. 
Draw-out shutters for dark-slides, iris diaphragms 
and Waterhouse stops, developing dishes up to 
about 15 in. by 12 in., and much larger flat 
trays (with an outer wooden casing) for silver 
baths, are made of this material. 

In process work, ebonite is useful for parts of 
etching machines which have to be exposed to 
the acid. 


EBONY STAIN 

Ebony stain (Stephens’s) is preferred to Indian 
ink by some pen-and-ink artists. It makes a 
good line, and dries with a glossy surface which 
photographs well. It has the drawback of not 
being waterproof, and of more quickly clogging 
drawing pens than does Indian ink, It is cheap, 
and if otherwise suitable it is worth while trying 
to waterproof it by adding a solution made by 
boiling together 2 oz. of shellac and }$ oz. of 
borax in 10 oz. of water, and straining. 


EBULLIOSCOPE (Fr., Ebullioscope; Ger., 
Ebullioskop) 

An apparatus for testing the purity of a liquid 
or solution by ascertaining the temperature at 
which it boils. When a liquid contains dissolved 
substances its boiling point is usually higher, 
and a concentrated solution has a higher boiling 
point than a weaker one. 


EBURNEUM PROCESS 

An obsolete process invented in 1865 by 
J. M. Burgess, of Norwich, in which a carbon 
or collodion transparency, transferred from a 
sheet of waxed glass, was backed up with an 
ivory-like mixture, which gave it the appear- 
ance of being on ivory. Burgess’s original 
instructions were, briefly, as follows:—A good 
collodion transparency is necessary, and the glass 
upon which it is taken should be waxed to 
facilitate stripping. Either an iron or pyro 
developer is used, preferably the following :— 


Pyrogallic acid . 3to6grs. 7 to14g, 
Citric acid : 7 5 ev 
Glacial acetic acid . 20 drops 42 ccs. 
Water T70z. £000 . "5, 


Fix with cyanide, well wash, and tone with 
gold. When dry, strips of paper are pasted 
round the plate on the back and then turned 
up so as to form a dish. The plate is placed 
level and coated with the following mixture at 
a temperature of 100° F, (38° C.) :— 


When set, the plate may be allowed to dry 
spontaneously and the film detached. The pro- 
cess was slow and difficult, for which reason it 
was little used. Imitation eburneum prints 
widely known as “‘ Ivorytypes ” (which see) were 
more popular. 


ECLIPSES, PHOTOGRAPHING 


The portrayal of the varying phases of an 
eclipse, whether of the sun or moon, is always of 
interest to the photographer. The exact times 
at which these phenomena will occur can always 
be ascertained a considerable time in advance 
from the almanacs, thus enabling the photo- 
grapher to prepare any special apparatus he may 
desire to fit up for the occasion, - 

Dealing first with eclipses of the moon, the 
chief interest in these lies in the gradual change 
in shape as the moon traverses the earth’s 
shadow. When fully eclipsed the moon may be 
either quite invisible, or showing of a more or 
less bright coppery colour. The most satis- 
factory manner of obtaining a picture of the 
eclipse with an ordinary camera is to set up the 
camera on its tripod and focus sharply; then 
swing until the moon is near one end of the 
ground glass. The end chosen should be that 
from which the moon’s image will travel in its 
motion across the sky owing to the earth’s 
rotation. This is always from east to west, so 
that, remembering that everything is inverted 
in the camera, the first exposure should be 
arranged near the right-hand side of the plate if 
the observer is in the northern hemisphere. 
Loa¢ the dark-slide with isochromatic plates of 
medium rapidity; draw the slide, and expose 
with the cap. Give about a quarter of a second 
exposure. After making one exposure, leave the 
apparatus as it stands, with slide still drawn, for 
say five minutes. During this interval the 
moon’s image will have travelled towards the 
left on the plate, and another similar exposure 
may then be given. Repeat this procedure at 
intervals of about five minutes until the eclipse 
is over. On developing, which will be exactly 
like the development of an ordinary subject and 
needs no special description, a series of pictures 
of the moon will be found extending across the 
plate, and of varying shapes, from full circle, 
through crescents to the dusky total eclipse. A 
pleasing variation to the above procedure may 
be made if the observer has a telephoto equip- 
ment, as he can with it obtain larger pictures 
of the moon’s phases, showing more details of the 
surface structure. It will not be possible, how- 
ever, to obtain the whole series of pictures illus- 
trating the progress of the eclipse on a single 
plate owing to the increased magnification. If 
the series is required, then several loaded plate- 
holders must be got ready to hand and the 
plates changed as found most convenient, 

With eclipses of the sun, the problem is some- 
what different, chiefly on account of the very 
great actinic power of even asmall section of the 
uneclipsed solar disc. If the eclipse is only 
partial, the arrangement described above for the 
lunar eclipse may be repeated except in regard 


Eczema Procurata 


to the exposure. This must be rendered as 
short as possible. If a focal plane shutter is to 
be employed, the slit in the blind must be made 
as narrow as possible, and the tension run up to 
the maximum. Should a diaphragm or cap 
shutter only be available, then it will be advis- 
able to stop down the lens to the smallest aper- 
ture possible and also use the shutter at its 
greatest speed. 

The greatest interest, however, becomes cen- 
tred in the solar eclipse which becomes total, 
the dark moon blocking out all the usual brilliant 
white disc. Then it is that one is able to see 
that wonderful appendage to the sun, the corona, 
and the ring of ruddy atmosphere, the chromo- 
sphere. On a small scale these features may be 
photographically recorded by means of cap 
exposures, but they will have to be fairly rapid, 
say a quarter of a second, owing to the rapid 
motion of the moon. With a small mechanical 
stand having provision for driving the camera 
at the same rate as the drift of the moon much 
longer exposures may be given, and the coronal 
extensions portrayed to a greater distance from 
the moon’s limb. Owing to the special nature 
of the coronal light isochromatic plates should be 
employed for this class of work, and, preferably, 
the most rapid variety available. For recording 
solar eclipses on a very large scale, special 
cameras with lenses of great focal length have 
been at various times employed. For example, 
cameras with lenses of 40 feet focal length were 
used by an American party under Professor 
Campbell in India. The lens was situated at 
the narrow end of a tube, propped up on the 
top of a wooden skeleton tower. The plate 
holder was in a canvas-covered portion near the 
ground, and in one case the moon’s motion was 
counter-balanced by moving the plate-holder by 
a simple form of clepsydra. 

One of the most interesting and instructive 
applications of photography to a total solar 
eclipse consists in the use of the prismatic camera. 
In its simplest form this is the ordinary camera 
with a simple prism adjusted outside the lens in 
such a position that the light from the eclipsed 
sun must pass through both prism and lens 
before it reaches the photographic plate in the 
camera. By this means is obtained a series of 
pictures of the sun’s surroundings, instead of a 
single one as before. Every different substance 
present in the sun’s atmosphere will show as a 
different ring or series of rings, and it is by a 
study of such photographs—or spectrograms, as 
they are technically called—that astronomers 
have been able to learn what substances are 
present in the solar atmosphere. In a particu- 
lar example of the prismatic camera, the lens 
aperture is 6 inches, and the focal length of the 
lens is 74 feet. There is a single large prism 
of 45° refracting angle rigidly attached outside 
the objective, and the whole instrument is 
fixed to a strong equatorial mounting driven 
by a delicately adjusted clockwork movement, 
so that exposures of any desired duration can 
be given. 


ECZEMA PROCURATA 

A name given to the skin disease caused by 
the metol developer. For further particulars, 
see under the heading ‘‘ Metvl.”’ 


207 


Edinol 


EDGING (Fr., Bordure ; Ger., Einfassung) 


In wet collodion negative making, especially 
for process work, the glass plates are generally 
edged with indiarubber solution to prevent the 
film from being washed off during the operations 
of developing, intensifying, etc. Albumen and 
gelatine are also used for the same purpose, but 
with these materials it is generally the practice 


Edging Brush 


to coat the plate all over as a substratum. A 
useful device for edging is shown above. A 
small camel-hair brush has a strip of wood 
bound to the side of it, and the two are pushed 
through a cork, which stoppers a bottle or test 
tube containing the rubber solution. 


EDGING NEGATIVES FOR CARBON 
PRINTING 


Negatives intended for carbon printing require 
an opaque margin, called a safe-edge. A narrow 
margin of the print must remain white, as 
otherwise it will be difficult to transfer the film. 
This opaque margin may be produced by painting 
the edges of the film with water colour, or opaque 
varnish may be applied to the glass side of the 
negative. Another method frequently adopted 
is to attach narrow strips of thin, opaque paper 
to the negative, or to a piece of plain glass. In 
the latter case this glass is placed in the printing 
frame outside the negative, and one glass may 
be used for many negatives. 


EDINOL (Fr. and Ger., Edinol) 

A developer, known also as ‘‘ Paramol,’”? under 
which name it was originally introduced in 
1901, but the two agents are stated by some 
not to be exactly the same. It occurs in a 
faint yellowish crystalline powder, having the 
formula CsH, OH CH,OH NH, and it is soluble 
in twelve times its weight of water. Its factor 
number is 20, and it therefore stands midway 
between the slow-working developers, such as 
pyro, hydroquinone, and adurol, and the quick- 
working developers, metol, amidol, etc. It can 
be used as a single-solution or a two-solution 
developer, and works well when combined with 
hydroquinone. Edinol is extremely sensitive 
to the action of bromide as a restrainer, so much 
so that from 10 to 30 per cent. of a saturated 
solution of sodium bicarbonate instead of 
bromide has been recommended in cases of 
over-exposure. It is clean-working and is par- 
ticularly suitable for bromide and _ gaslight 
papers and transparencies. The formule for 
one-solution and two-solution developers are 
as follow :— 

One-solution 


Sodium sulphite . 2 OZ, 200 g. 

Water : ‘ tie a cea 500 ccs, 
Dissolve and add— 

Edinol : A $ oz, 50 g. 

Sodium carbonate ee 250 ccs, 
and then add water to make 10 oz. ‘his forms 


a concentrated developer, and for use is diluted 
with from five to ten times its yolume of water. 


Edison’s Kinetoscope 


Two-solution 


A. Sodium sulphite . 2 oz. 100 g 
Edinol . 96 gers. 10°; 
Water to 20 0Z 1,000 ccs 

B. Sodium carbonate . 10 % sol.; or 
Potassium carbonate «| § % sol, 


Use equal parts of A and B. Sodium carbonate 
works slowly, and for quicker working potas- 
sium carbonate may be substituted for it. (For 
use combined with hydroquinone, see ‘‘ Devel- 
opers, Mixed.’’) 


EDISON’S KINETOSCOPE 
scope.’’) 
EDWARDS’S FORMULA® 


These include a one-solution intensifier made 
up from the following :— 


(See ‘ Kineto- 


A. Mercuric chloride 60 gts. 3°98 
Water : . 8 oz. 227-CCs 

B. Potassium iodide . 180 gts. 11'7 g. 
Water ; d 2-02, 57 ccs 

C. Sodium hyposulphite 120 grs. 7g. 
Water . é 2 OZ. 57 ccs. 


When all are dissolved add A to B, shake well 
and add C; allow to stand for an hour or two 
before use. Soak the negative in this until 
intensified, and then immerse in a “hypo”’ fixing 
bath for half a minute, finally washing well. If 
local intensification is required, the solution 
may be applied to the parts with a camel-hair 
mop or a pad of cotton-wool. Edwards's 
reducer or clearing bath is used chiefly for 
removing yellow stains from negatives that have 
been developed with pyro. The formula is :— 


Alum . ‘ : ° I Oz. 55 g. 
Ferrous sulphate . mois TOs, 
Sulphuric acid I drm. 6°25 ccs. 
Water 20 OZ. 1,000 ,, 


This gives an apple-green solution, which is used 
after fixing and washing. It keeps well if the 
used liquid is not returned to the stock solution. 
Another formula due to Edwards is given under 
the heading “‘ Redeveloper.” 


EFFECT (Fr., Effet ; Ger., Wirkung) 

The general impression given by a print apart 
from any examination of its details. It depends 
mainly on the disposition of its principal masses 
and its chiaroscuro (which see). 


EFFLUVIOGRAPH 


An invention by Mons, Tommasi, in 1886, by 
the use of which all the effects of photography 
were obtained through the electric effuvia or 
obscute discharge. Two metal brushes, placed 
parallel in front of one another, were each con- 
nected to the pole of a Holtz machine. A dry 
plate of about the same height was placed per- 
pendicularly to the brushes; and on the dis- 
charge taking place in darkness an image was 
obtained by radiations. 

The term effluviography is sometimes applied 
to images obtained by what is more commonly 
known as vapography (which see). 


EGG, WHITE OF (Fr., Blanc des eufs, Albu- 
mine ; Ger., Frisches Eiweiss, Albumin) 
Commonly referred to in photographic pro- 
esses as albumen (which see). First used for 


208 


Eikonogen Printing Process 


coating glass plates by Niepce de Saint-Victor 
in 1848. About 1866 it was largely used for 
albumenised paper, and one maker stated at 
the time that he broke 2,000 eggs daily, merely 
to obtain the whites. Mayall, whose albumen 
negative process was widely used, stated that 
the white of a duck’s egg is more sensitive than 
that of a hen’s egg, and that the white of a 
goose’s egg was mote sensitive than either. 
In process work the whites of eggs are largely 
used for making up the albumen-bichromate 
solution in preference to dried albumen. 


EGYPTIAN VIGNETTES (See ‘Black Vig- 
nettes.’’) 


EIKONOGEN (Fr., Iconogéne ; Ger., Etkonogen) 

A developer introduced by Dr. M. Andresen 
in 1889; it appears in a yellowish white powder 
or yellowish crystals when fresh, but rapidly 
changes to a brownish tinge. Its formula is 
CioH; (OH)NH,SO,ONa. It is sparingly 
soluble in water, but readily so in the presence 
of alkalis, especially when heated. It can be 
used in a one-solution or a two-solution form, 
and is suitable for all kinds of plates and bromide 
and gaslight papers. It is widely advocated for 
very rapid exposures, for which the following 
one-solution mixture, which is ready for use, is 
particularly suitable :— 


Eikonogen . ‘ - 100 gfs, 20 g. 
Sodium sulphite . + (SOG ee 40 ,, 
Sodium carbonate + 21GO tas 20). 
Potassium bromide . 65 ,, 1 tr 


1,000 ccs. 


The small quantity of bromide added appears 
to increase the density of the negative, but where 
there is a suspicion of undet-exposure, and when 
soft portrait negatives are desired, it is better 
omitted. Bromide acts very powerfully with 
eikonogen, and further additions in cases of 
ovet-exposure should be made cautiously. The - 
following is the formula for the two-solution 
form :— 


A. EHikonogen . I OZ. 50 g 
Sodium sulphite hee 200 ,, 
Water . fa ai 72 pe 1,000 ccs, 

B. Sodium carbonate : ae 150 g. 
Water . ‘ Pee We 1,000 ccs. 


For use, mix 1 part of A, 1 part of B, and 
2 parts of water. Potassium carbonate may 
be used in place of the sodium in the B solution, 
and a more energetic developer obtained. When 
eikonogen is used for wet plates they generally | 
need to be intensified, preferably with pyro- 
silver, (For an eikonogen-hydroquinone com- 
bination, see “* Developers, Mixed.”’) . 


EIKONOGEN PRINTING PROCESS 

A process invented in 1895 by A. Frey, of 
Paris. Aniline, or toluidine, is treated with 
sulphuric acid, and the almost colourless pro- 
duct is dissolved in warm water. A mixture of 
this solution with eikonogen, applied to albumen 
paper, gives a reaction on exposure to light. 
Cherry or blackberry juice is bleached by mixing 
with eikonogen solution, but when paper coated 
with the mixture is exposed to light the colour 
returns. In the same way, several iron, copper, 
and tin salts, when mixed with eikonogen, are 


JOPPA epee 


BENNETT, 


WwW 


BY H 


CAUX 


CAUDEBEC-EN 


CHURCH OF NOTRE DAME, 


PHOTOGRAPHY (EXTERIOR) 


ARCHITECTURAL 


Eikronometer 


Sensitive to light. Freshly prepared potassium 
formate with eikonogen also yields a sensitive 
substance. 


EIKRONOMETER (Fr., Eikvonométre ; Ger., 
Etkronometer) 
An early form of the Watkins dark-room 
clock. (See ‘‘ Clock, Dark-room.’’) 


ELECTRIC INKLESS PRINTING 

A pfocess invented by W. Friese-Greene, in 
which the electric current was made to pass 
through the type forme and the impression 
cylinder of an ordinary letterpress printing 
machine. The paper was treated chemically, 
probably with an iron salt, and when impressed 
on the type was darkened by the electric action. 


ELECTRIC LIGHT (Fr., Lumiére électrique ; 
Ger., Elektrisches Licht) 

The electric light is the most practically useful 
artificial illuminant for photographic purposes. 
Where public mains are not accessible, a small 
dynamo, driven by a gas-engine, offers the most 
convenient means of installation. Apart from 
the initial expense of the dynamo and engine, 
this is naturally more economical than the public 
supply, though involving greater trouble and 
attention. The switches should be such as will 
stand hard wear and rough usage, and an adjust- 
able resistance is an advantage. ‘There are four 
principal types of lamps—the arc, the incan- 
descent or glow lamp, the Nernst lamp, and the 
mercury vapour lamp. In portraiture, the arc 
lamp is most used. For studio employment and 
for ordinary black-and-white copying, the 
enclosed are is best, but for photographing 
colour the open arc is superior, These two 
patterns are fully dealt with under the heading 
*“Arc Lamps.” Flame arc lamps, in which a 
brilliant golden yellow light is obtained by 
incorporating metallic salts in the carbons, or 
by introducing a central core of such salts, have 
also attracted some attention among photo- 
graphers, it having been stated that colour values 
are better reproduced with them. A plate 
sensitised for yellow has, of course, to be 
employed. An arc lamp in use should not be 
examined or adjusted without a piece of smoked 
yellow glass before the eyes, or goggles of the 
same material. 

The incandescent glow lamp is yellower and 
less actinic than the arc, but a number of these 
suspended inside a dead white spherical or para- 
bolic reflector, having a muslin diffusing screen 
in front, can be used for portrait work, giving 
a soft and pleasing lighting. Several lamps of 
this kind are on the market. Ruby and orange 
glow lamps are much used in the dark-room. 
The new metallic filament lamps have greatly 
improved the efficiency of incandescent electric 
lighting, yielding better illumination with less 
current than carbon filament lamps, 

The Nernst lamp makes use of a thread of 
yttrium and zirconium oxides, and similar 
metallic earths. These lamps are employed 
with the optical lantern and for enlarging; they 
are economical of current and carry their own 
resistatices. 

The mercury vapour lamp is dealt with under 
its own heading. It requires very little current, 

14 


209 


Electrograph 


and is a useful light for printing, copying, or 
enlarging. A certain prejudice exists against 
its employment in portraiture owing to its 
unpleasant colour, due to the absence of red 
rays, but this is easily remedied by using one or 
two ruby glow lamps in addition. 

For copying, etc., the nearness with which the 
lamp can be placed to the easel is of import- 
ance from an economical standpoint, other 
considerations being equal. Thus, the enclosed 
arc cant be brought closer than the open arc, 
the flame arc still nearer, and the mercury vapour 
lamp nearest of all. 

In process work, the electric arc light is invari- 
ably used for copying in preference to daylight. 
(See “Arc Lamps.’’) Mercury vapour lamps 
are also used to some extent. Incandescent 
electric lamps are not sufficiently powerful. 


ELECTRIC LIGHT FOR OPTICAL LAN. 
TERN (See ‘‘ Optical Lantern.’’) 


ELECTRIC RADIATIONS (See 
Photography.’’) 


ELECTRIC TELEPHOTOSCOPY (See 
“Transmission of Photographs Electric- 
ally.’’) 


ELECTRO 
A common abbreviation of the term “ Elec- 
trotype’”’ (which see). 


ELECTRO ETCHING 

Numerous processes have been put forward 
at various times for etching by means of the 
electric current, but none has come into regular 
commercial use. The earliest was a method of 
etching the daguerreotype plate. Fizeau gilded 
the image by depositing gold upon it, and then 
etched the parts not covered by the gold, which 
acted as a resist. Grove, Donne, and others 
iether engraved plates in this manner, per- 
orming the etching by galvanic action, but the 
difficulty of biting the delicate daguerreotype 
image to a sufficient depth and obtaining the 
requisite ink-holding grain soon led to the 
abandonment of the method. Prof. Jacobi, in 
1839, engraved line plates into relief by electric 
etching, and about the same time Thomas 
Spencer, of Liverpool, described a process of 
galvanic etching by coating copper plates with 
a resist ground and scratching lines through it. 
In later times J. W. Swan used electric etching 
for photograyure plates. Images scratched with 
needle-points through an etching ground have 
often been successfully etched. Sanger Shep- 
herd some years ago described a process of etch- 
ing a bitumen print on copper by depositing gold 
on the parts laid bare by development and 
etching the other parts. Dr. Strecker has 
patented a process for electric etching with the 
solution of a zinc salt. Zinc, copper, and steel 
have been successfully etched, but the process 
is slower than ordinary etching, and does not 
appear to have any advantages. 


ELECTROGRAPH (Fr., Electrographe ; Ger., 
Elektrograph) 

An apparatus for the telegraphic transmission 

of photographs, invented conjointly, in 1901, by 

H. R. Palmer, M. E. T. Mills, and Dr. W. P. 


- 


“ X-ray 


Electrogravure 


Dunlany. The receiving and transmitting 
machines are identical in construction, and may 
be used alternatively. The transmitter carries 
a zinc enlargement of a half-tone plate, curved to 
fit a cylinder, the depressed or etched portions of 
the plate being filled with an insulating material. 
Over the cylinder a stylus is made to travel, 
much after the manner of a phonograph stylus. 
At the other end of the wire, the receiving cylinder 
is fitted with a pen, which travels at the same 
rate as the transmitting stylus over a sheet of 
paper placed beneath. When the stylus is in 
contact with metal the circuit is completed, and 
the pen of the receiving instrument traces a dot 
ot line corresponding with that on the zinc plate ; 
but when the stylus touches the insulating 
material in the etched portions the circuit is 
broken, and no mark is made by the pen. Asa 
consequence, the picture on the half-tone plate is 
reproduced at the receiving end, and from the 
copy a smaller plate, suitable for press use, may 
be made by reduction in the usual manner. Each 
instrument is provided with a pen as well as a 
stylus, and either may be used at will. 


ELECTROGRAVURE 

A process invented by Jos. Rieder for etching 
on steel by galvanic means. It was shown at 
the Paris Exhibition of 1900. 


ELECTROLYTIC BREAK 
Breaks.’’) 


ELECTRO-PHOTOTYPY 

A name given to Sutton’s process (not used. 
commercially) of making half-tone printing 
blocks. A half-tone negative was made by 
photographing through a ruled screen on to a 
gelatine plate. After being developed, and 
before it was completely dry, the plate was 
heated, this having the effect of swelling the 
dots into high relief. The plate was then used 
as a mould for electrotyping. 


ELECTROTINT 
A fancy name given to the half-tone process 
by an American firm. 


ELECTROTYPE (Fr., Electrotype, Galvano; 
Ger., Galvano, Galvanische Riederschlag) 


A copy or reproduction of a relief surface 
made by the electrotyping process. 


ELECTROTYPING (Fr., Electrotypage, Galvano- 
plastie ; Ger., Galuanoplastik) 

A process by which engraved plates, type 
formes, etc., are reproduced. They are pressed 
into a layer of beeswax, the resulting mould is 
blackleaded by brushing or by spraying with a 
solution of blacklead, to make the surface con- 
ductive, and the mould is then suspended in a 
solution of copper sulphate, a copper plate being 
suspended opposite and near to the mould to 
form an anode. The two are connected to a 
source of electric current, and copper is then 
deposited in a thin shell on the mould until 
thick enough to be stripped off. This shell is 
filled up at the back with type metal to give it 
sufficient thickness and solidity, and after being 
planed at the back and mounted on a wood or 
metal block is ready for printing from. 


(See ‘* Contact 


210 


Element 


Photographic reliefs in gelatine have also been 
electrotyped. (See “‘ Swelled Gelatine Process.’’) 

The late G. Scamoni, of St. Petersburg, suc- 
ceeded in electrotyping from the image of a wet 
collodion negative. Nickel, nickel steel, iron, 
brass, and other metals have also been success- 
fully deposited by electrotyping. In the Ord- 
nance Survey Office, Southampton, original 
engraved maps are reproduced by electrotyping. 
The copper plate is silvered to prevent the 
copper from adhering, and a thick shell is 
deposited. This is in relief, and forms the 
matrix from which any number of duplicates 
may be made. The matrix is silvered and 
deposited on in the same way as upon the 
original. Major-General Waterhouse, when at 
the Survey of India, successfully electrotyped 
from a photographic carbon image developed 
on the copper plate. (See also “‘ Daguerreotypes, 
Electrotyping.”’) 


ELECTROTYPY 


A process of reproducing daguerreotypes by 
electro-deposition. 


ELECTRO-ZINCOGRAPHY 
A process of engraving on zinc in which the 
electric current is used. 


ELEMENT (Fr., Llément ; Ger., Element) 


This term has been applied by chemists to 
those substances which cannot, by any known 
means, be split up into other and simpler forms 
of matter. The following table is a list of them, 
with the symbol and atomic weight of each. 
The symbol, it may be explained, is the chemist’s 
shorthand or grammalogue, whilst the atomic 
weight is that in which each element combines 
with others to form salts or compounds. Thus 
the chemist writes AgNO, for silver nitrate, 
and this formula means that there are 108 parts 
of silver, 14 parts of nitrogen, and 48 parts of 
oxygen combined to form 170 parts of silver 
nitrate. If now it is wished to form silver 
bromide from this, using potassium bromide, 
the equation or shorthand for the decomposi- 
tion which would occur would be written :— 


AgNO, + KBr = Ag Br + K NO, 


108,14,48 39,80 108,80 39,14,48 
170 + 119 = 188 + 101 


and this shows that 119 parts of potassium 
bromide would be required to convert 170 parts 
of silver nitrate, and the result would be 188 
parts of silver bromide, with 1o1 parts of potas- 
sium nitrate as a by-product; and no matter 
what actual weight of silver nitrate was used, 
the combination would always take place in 
the above ratio—I70: I19. 


Name Symbol Atomic weight 
Aluminium . Ray: vie + ee 
Antimony (Latin : 

Stibium) ae se 
Arsenic . . fas “i Sas 
Barium ; saiBa i "az 
Beryllium . site s gl 
Bismuth ° ¢ Slo. - 208 
Boron ° ae ° I 
Bromine ° Bee cia & 
Cadmium ‘ s? GS ont Ike 


“glass a ls 


Element 


Name Symbol Atomic weight 
Cesium ° « SBS aad $2.5 
Calcium a ik Oe a 2 es 
Carbon . . >a, Sa ; 12 
Cerium . . Ay ©. BF - 140 
Chlorine : o, eo 2. ass 
Chromium . oo Ree ; 52 
Cobalt . : ed. Os oe El 
Copper (Latin : 

Cuprum) . a, oa eA 


Didymium ., Re Bs ee 
Erbium. . ne eae 7 | a6 


Fluorine 4 Ae ee 2.5 be 
Gallium : ar ABs a oe 
Germanium . pe ie cums eia 
Gold (Latin: durum) Au. MALS 
Helium. : . He - 4 
Hydrogen. ai = ee é I 
Indium : lal 1s Sa oie (DS 
Iodine . : a! ay ba SERS 
Iridium : mt A a AOS 
Iron (Latin: Ferrum) Fe . eh AES 
Lanthanum . .” a. PH ce 
Lead (Latin: Plum- 

bum). ; ee 209 
Lithium ; Pity sh ae ; ye 
Magnesium . . Mg cea 
Manganese ges 6s 55 
Mercury (Latin : 

Hydrargyrum) Hg. «200 
Molybdenum Pe he OO 
Nickel . : Logie tap he 
Niobium : oat Ny, « ih 
Nitrogen ean.) s : 14 
Osmium ‘ Sta, aa eae 2 

Oxypen. Aa 8 eee Cae 
Palladium . Peg <3 Be 6. LO 
Phosphorus . A aa a eh 
Platinum ‘ gg op a re oie srt 
Potassium (Latin: 

Kalium) . us ee 
Rhodium . pie aS ean DOR 
Rubidium . Shy | ae oe 
Ruthenium . es SA ge «1035 

Ramah | ee A mS a 
Scandium : iy SR a Lin Pte 4 
Selenium . pe". piu 7D 
Silicon . ; et ae Pee §, 
Silver (Latin: Argen- 

tum) . : Se A 108 
Sodium (Latin : 

Natrium) . ee Ee ie, 23 
Strontium . - “or aes 
Sulphur : 2 yw So 

~Testalim  . Alea: Sa - 182 
Tellurium. . ae % pres 
Thallium - A ge 6 - 204 
Thorium : rages ae * 232 
Tin (Latin: Stannum) Sn . skid 
Titanium ; Aes iat.) 
Tungsten (Latin: 

Wolfrunium) 5 Oy » 84 
Uranium : oe +240 
Vanadium . Ao Sige Sa aS 
Ytterbium . ees Pe i 
gine. : ee ae ata eek 
Zirconium . he | ae OO 


The Latin names in brackets are included to 
show the derivation of the symbols. Only the 
atomic weights generally used are given, as these 


2I1 


Emulsion 


are continually under revision, and some are 
still in doubt, although only to the first or second 
place of decimals, The newer gases and some 
of the latest discovered elements—such as 
radium, etc.—are not included. 


ELEMI (See ‘“ Gums and Resins.”) 
ELIMINATORS (See “‘ Hypo’ Eliminators.’’) 


ELLIOTYPE 


_ A process of painting a picture upon glass, 
in body and transparent colours, and printing 
therefrom as though it were an ordinary nega- 
tive; named after its introducer. It was never 
largely used, and is now obsolete. 


EMERY (Fr., Emeri ; Ger., Schmirgel) 

An exceedingly hard mineral, varying slightly 
in colour, a compact variety of corundum, and 
very generally regarded as an iron ore. Chemic- 
ally it consists of alumina, silica, and iron. Its 
chief source is the Isle of Naxos. It is reduced 
to powder and used for grinding and polishing 
metal, glass, etc. Opticians use it for the first 
rough grinding of lenses. Square sticks of 
emery, called emery files, are sometimes used 
by wet collodion workers for taking the sharp 
edge off glass plates; but carborundum sticks 
have been found better. Emery is sometimes 
used in the form of a very fine powder instead 
of pumice powder for cleaning copper and zinc ; 
and collotype workers grind the surface of their 
thick glass printing plates with fine emery to 
give a matt surface to which the film can adhere. 


EMETICS (See “ Poisons and Their Antidotes.’’) 
EMISSION, NODE OF (See “* Nodal Points.’’) 


EMULSION (Fr., Emulsion ; Ger., Emulsion) 

A liquid, usually viscous, containing in 
suspension an insoluble body in an extremely 
finely divided state. Plates, films, and bromide, 
gaslight and printing-out papers are coated 
with emulsions. To such perfection has the 
commercial manufacture of these articles attained 
that it will hardly pay the average worker to 
prepare his own; but from an educational point 
of view the manufacture of emulsions is extremely 
valuable. In the following notes only tested 
formule are given, and it must be clearly under- 
stood that perfection is only attainable after 
considerable experience, and the tyro must not 
expect to prepare either papers or plates as 
excellent or as fast in working as those com- 
mercially obtainable. 

The various stages in emulsion making will be 
outlined, and the reasons for each step explained. 
Let it be assumed, therefore, that it is wished 
to make a silver bromide gelatine emulsion. 
The bromide is formed by double decomposition 
or chemical interchange between an alkaline 
bromide, usually potassium or ammonium, and 
silver nitrate. If aqueous solutions of these two 
salts were mixed in a haphazard fashion there 
would certainly be obtained a coarse, granular 
form of silver bromide which would at once sink 
to the bottom of the vessel, and there might be 
an excess of either silver nitrate or bromide. To 
prevent the immediate deposition of the bromide, 


Emulsion 


and to obtain a fine grain, a vehicle—gelatine— 
is added to the alkaline bromide solution, and 
the fineness of grain largely depends upon the 
proportion of gelatine used. If too much gela- 
tine, or too hard a kind, be used during mixing 
it is difficult to obtain high speed, as the gelatine 
acts as a mechanical restrainer; on the other 
hand, if too little is used, a coarse granular 
deposit is formed, and the emulsion tends to 
fog and thinness. When an alkaline bromide 
and silver nitrate are mixed together they com- 
bine in definite proportions according to their 
molecular weights. The molecular or combining 
weight of potassium bromide is 119, and that of 
silver nitrate is 170. If these quantities were 
weighed out exactly, whether in grains, outices, 
pounds, or tons, or grammes or kilogrammes, 
exactly 188 parts of silver bromide would ‘be 
formed, and there would be found in the water 
neither silver nitrate nor potassium bromide ; 
but the slightest error in weighing might give 
an excess of silver nitrate, which would be 
fatal to the emulsion in development. It is 
customary, therefore, to use an excess of bromide 
or other salt in all emulsions intended for develop- 
ment; this excess varies in most formule, and 
is governed by the process used, the quality of 
the gelatine and the speed required. Some 
gelatines will give perfectly clean emulsions with 
a much smaller excess than others. Then, as 
one of the prime uses of the excess of bromide 
is to keep the emulsion free from fog, a reasonable 
excess is useful on this account, and increase 
may make an otherwise foggy-working formula 
satisfactory. Of recent years it has been con- 
sidered that an increased excess of bromide 
tends to give faster emulsions for negative work, 
but it has at the same time a tendency to pro- 
duce thinness in the high lights. A normal 
ratio is 100 of silver nitrate to 80 of potassium 
bromide, though it will be seen that the ratios 
given in the formule vary from this in some 
cases. 

When first mixed the emulsion is very slow, 
no matter what formula is used, and would be 
quite unsuitable for anything but lantern plates. 
It is therefore subjected to a “ ripening ”’ process, 
either by continued application of heat or the 
use of ammonia. Exactly what occurs during 
ripening is a matter of doubt, but it is generally 


212 


Emulsion 


assumed that the silver bromide grain increases 
in size and that this increase is accompanied 
by greater sensitiveness to light; the change 
is probably more of a physical than chemical 
nature. 

It has been already stated that there is a 
chemical interchange between the silver nitrate 
and bromide, and this is represented by the 
following equation, which may be said to be 
the chemist’s shorthand method of explaining 
what occurs :— 


silver nitrate pot. bromide silver bromide _ pot. nitrate 
170 119 188 IOl 


The figures here are the molecular or com- 
bining weight, and, as has already beem 
explained, 170 parts of silver nitrate combine 
with 119 of potassium bromide to form 188 parts 
of silver bromide and 101 parts of potassium 
nitrate. Alkaline nitrate thus formed must be 
got rid of, and this is the purpose of the washing, 
which also removes the excess of alkaline 
bromide and the ammonia, if this latter has been 
used for ripening. Were these salts not washed 
out they would crystallise out on the plate 
during the process of drying after coating, and 
either prevent the access of light, or give rise to 
crystalline markings which would show in the 
negative. 

There are two distinct systems of making 
emulsions: the acid or boiling process and the 
ammonio-nitrate process. The former, as a 
rule, is used for somewhat slow emulsions, and 
the latter for the faster negative kinds. As to 
the highest speed obtainable by the acid process, 
no definite data are available, but certainly 
200 H. and D. may be considered the limit, whilst 
by the ammonia process from 300 to 400 H. and. 
D. can be reached. In the acid process the 
mixing and the ripening are effected in an acid 
gelatine solution, whilst in the other process 
either the whole or part of the silver nitrate is 
converted into ammonio-nitrate of silver. For 
amateur work the ammonia process is somewhat 
easier, and, if excessive speed is not required, 
nice clean emulsions, giving good density, can 
be obtained. 

Before treating further on the actual mixing 
of the emulsion, it should be stated that the 


TABLE I 


Ld 

Sz 

= V 

ss 
Ammonium bromide a . 98 
Potassium bromide . i ; I19g 
Sodium bromide . ° F . 103 
Ammonium chloride 6 53°5 
Sodium chloride . ‘ : 58°5 
Ammonium iodide . a ‘ x 143 
Potassium iodide . 5 ‘ ;. 166 
Sodium iodide * ‘ ‘ 150 


Weight of AgNO; 
vequired to convert 


8 SV sys LQe s 3c 
~ ~~ YY E Ly 
3 |33" | $33) 429) eee 
2/38. | 738 | Reng | Bs 
eV > SS Qa 
c oF e one os gs 3. rs 
v8 mSS Bs 33 #3 'S 
Ss | S885 | 38°38 | S888 } S88h 
2 | 288q | S838 | seas | Sex 
= & = = 
1°734 576 1-918 521 ; 
I°427 700 1°578 633 1°106 
1°620 606 I a8 548 
3°17 315 2°682 373 } 8 
2-906 344 2453 408 44 
853 1620 617 
1+023 977 1°415 707 1°382 
I°I33 882 1566 638 


Emulsion 


alkaline bromides and iodides are interchange- 
able, though as a rule that given in a formula 
should be adhered to; still, the accompanying 
tables, compiled by Ackland, will be found ex- 
ceedingly useful, as they allow of the easy cal- 
culation of the necessary amount of haloid for 
any quantity of silver, or the substitution of one 
for another, 

Table I. enables the worker to calculate the 
weight of haloid to convert any given quantity 
of silver, or, vice versa, the quantity of silver 
haloid produced from every grain of haloid, or 
the weight of silver haloid produced from every 
gtain of silver nitrate. If, for instance, the 


formula is :— 
Potassium bromide 150 
Potassium iodide ; > 10 
Ammonium chloride . oo eS 
Gelatine . : : 200 


The quantity of silver required to saturate the 
above can be calculated by taking the figures 
in the third column and multiplying by the 
above. Thus :— 


Potassium bromide 150 X 1°427 = 214°:05 
Potassium iodide O-xX 17029) = 10°28 
Ammonium chloride 25 x 3°177 = 


79°425 


Weight of silver nitrate required 303-705 


The fourth column enables the worker to cal- 
culate readily what excess of soluble haloid 
there may be present in the emulsion; whilst 


213 


Emulsion 


considerable influence on the final result, both 
as regards speed and density. If the speed 
required is approximately obtained in the first 
process of cooking, then pouring out the emul- 
sion into flat pans to the depth of about 1 in. 
will quickly arrest the ripening action, especially 
if the pan or dish is stood in cold running water. 
In summer-time it is even advisable to pack ice 
around the pan, which for such small quantities 
as given in these pages may be a clean (most 
important) 15-in. by 12-in. dish. On the other 
hand, if the emulsion is allowed to set in its 
mixing pot, greater speed is obtained, especially 
when amimoniacal emulsions are made, because 
the heat is longer retained, and there is less 
chance for the escape of the ammonia, It is as 


well, however, in this case to cool the bulk of 


the emulsion by running cold water around the 
pot and constantly stirring ; ice water, too, may 
be used, but care must be exercised, as when an 
emulsion is poured out into flat, ice-cooled pans 
to set there is danger in the case of negative emul- 
sions of a want of density in the highest lights. 

Stil more important with regard to the 
density and speed of the emulsion is the lapse 
of time between the setting and washing; and 
in the case of negative emulsions the speed may 
be nearly doubled, and consequently the density 
of the high lights increased, by allowing the 
emulsion to stand in the solid state in cold for 
twenty-four to forty-eight hours. Except where 
otherwise advised, the normal time is about 
twelve hours; that is to say, a negative emul- 


TABLE Il 


es 5 
“oS 28 
ues 2‘ 
oS 2: 
=: zs 
ss Ls 
= 


Ammonium bromide . : 
Potassium bromide F : 
Sodium bromide . 
Ammonium chloride 

Sodium chloride . 


° e ° e e e e e 


Ammonium iodide - ‘. 
Potassium iodide : f 
Sodium iodide . P n 


ee % 5 S = 
“SS s$ . vy . bid LY) 
aN SS = S38 | ss 
Ss = oS a2'"S Ss 
es 3.2 =. Ces ies 
Ss os =: ea 2.2 
= 0 Ns = Ry ip) 
x sy 


columns 5, 6, and 7 enable him to work back 
when he has determined on a fixed content of 
silver haloid. 

Table II. is extremely useful for finding the 
weight of one haloid that will replace another. 
Supposing, for instance, that it is desired to 
replace 80 grs. of ammonium bromide with the 
sodium salt; then in the first vertical column 
headed ‘‘ammonium bromide” there will be 
found against sodium bromide 1-051, which is 
the weight of this salt that will convert as much 
silver nitrate as one grain of ammonium bromide. 
Therefore 1:°051 x 80 = 84:08 would be the 
quantity of sodium haloid to use. 

Before entering into the making of emulsions 
it may be as well to consider the subsequent 
operations first, as they play an important part 
in the quality of the finished emulsion. The 
method adopted for setting the emulsion has 


sion made one evening is ready the next morning 
to be broken up. and washed. 

The easiest method of breaking up small 
quantities of emulsion is to use coarse-meshed 
canvas, the mesh being about jin. square. The 
emulsion should be coarsely cut up by means 
of a silver knife (do not use a steel one), or 
scored through with a wide-pronged silver or 
plated fork, and then put into a sheet of the 
canvas, the ends of the latter being gathered 
together so as to form a bag. The bag is held 
under the surface of a dish of clean water and 
squeezed round and round so as to force the 
emulsion through the mesh. Failing the canvas, 
a fork can be efficiently used if the emulsion has 
been set in a dish, as it can be scored longitudin- 
ally and then across at right angles so as to cut 
it up into little cubes, which should not be too 
small, as otherwise they pick up too much water. 


Emulsion 


Commercially, when large quantities of emulsion 
have to be treated, a power or hand press is 
used, and the emulsion forced through a perfor- 
ated plate. 

After shredding, the emulsion is washed. 
According to the quantity to be treated, washing 
may be effected either in flat trays or by means 
of a calico or linen bag’ and a deep jar. In the 
first case, a sheet of linen should be placed over 
the dish or tray, and the emulsion placed in 
it and a stream of water allowed to run in at 
one corner and out at the diagonally opposite 
corner: it is as well to raise slightly that end 
of the dish at which the water flows in. In the 
case of the bag method a square of linen should 
be gathered up into a bag, the emulsion placed 
therein, and some stout string tied round with 
a sufficiently long loop to pass over a stick 
that rests on the mouth of the jar and allows 
the bag to hang down in the water. By this 
method the soluble and detrimental salts 
formed in the emulsion diffuse out into the 
water. Whichever method is adopted, it is 
important that the water should be frequently 
changed, and it is advisable to squeeze the 
emulsion gently at intervals so as to press out 
the water. 

There is great diversity of opinion as to the 
best duration of washing, some workers main- 
taining that from eight to twelve hours is not 
too long, whilst others reduce the time to two 
hours or even less. The disadvantages of pro- 
longed washing are that the emulsion, par- 
ticularly in hot weather, picks up a large quan- 
tity of unnecessary water which, unless an extra 


quantity of gelatine is added afterwards, renders , 


the emulsion so sloppy that it is difficult to coat 
it on glass, and, further—particularly with rapid 


negative emulsions—the ripening process goes © 


on,-and as the soluble bromides in excess are 
being removed, there is great danger of fog 
ensuing. From very careful tests the writer 
has found that all emulsions can be thoroughly 
washed by repeated changes (about twelve) of 
water in two hours, and small quantities—par- 
ticularly if the weather is warm—can be ‘thor- 
oughly washed in one hour. The washed emul- 
sion should be allowed to drain well, and is then 
ready for melting. 

The emulsion shreds should be placed in a 
pot in a water bath at 90° F. (about 32° C.) and 
the temperature gradually raised to 120° F. 
(nearly 49° C.), at which temperature the final 
quantity of gelatine should be added and the 
whole well stirred till the gelatine is dissolved. 
It is just as well to keep the emulsion at this 
temperature for at least half an hour, and it 
can then be filtered through clean felt jelly- 
bags, ot, failing these, swansdown calico or 
Canton flannel, previously washed to remove 
any dressing. If there is any difficulty in getting 
the emulsion to pass through the material, 
pressure may be applied by squeezing with the 
hands, but usually, with the emulsion at the 
temperature’ stated, there is no trouble pro- 
viding the filter is first wetted with hot water 
and well wrung out. ad 

GELATINO-CHLORIDE OR P.O.P. EmMursion.— 
The simplest form of gelatine emulsion is that 
used for P.O.P., and the following formulz will 
give excellent results :-— 


214 


Emulsion 


Valenta’s Formula 


A. Silver nitrate . . 3097 gEs.) gzeg. 
Citric acid ; 54 eae 
Hot distilled water 3 OZ 160 ccs. 

B. Hard emulsion gela- 

tines). 5 ; . O22'er8 96 g. 
Distilled water 4) Shoe 7O0O ccs. 


Allow to soak for half an hour, and then melt 
in a water bath at 120° F. and add— 


Cc. Ammonium chloride. 28grs. 28g. 
Tartaric acid . éjv, a as 2h 
Sodium bicarbonate 14 ,, i). ae 
Alum : Pye 8 8) Th 
Distilled water 302, \ EAG ce: 


The ingredients in solution C must be dis 
solved in the order given, and care should be 
taken to use a sufficiently large vessel, as brisk 
effervescence ensues. Both B and C should be 
brought to 120° F. (nearly 49° C.) and mixed, 
and then A, at the same temperature, added 
slowly and with constant agitation. Allow the 
emulsion to stand for from two to four hours in 
a water bath at 110° F. (about 43° C.) with occa- 
sional stirring, and then add— 


Alcohol R ‘ . 15 drms. 100 ces. 


and filter through glass wool or two thicknesses 
of Canton flannel or one thickness of swansdown. 
Care must be exercised as to the light used, as 
the fluid emulsion can readily darken in colour 
whilst digesting even in strong gaslight. The 
duration of digestion or ripening is dependent 
on the speed required. If coated when freshly 
mixed, the emulsion is slow and gives rich and 
vigorous prints; if, on the other hand, it is 
ripened for four hours it becomes much more 
rapid, and gives a longer scale of gradation. If 
it is desired to obtain a paper that will keep for 
some time without discoloration, an equal 
quantity of citric acid to that given above 
should be added after digestion. 

Another excellent formula is the following :— 


Wade's Formula 


A. Ammonium chloride. 25 grs. 26g. 
Rochelle salts . ae 1 et 2, 
Alum ; ‘ Mt Ae ce yr 
Distilled water o SeOZe Shes cos: 

Dissolve, and add— 

B. Gelatine . . 820grs, 86g. 

Distilled water 15 OZ “78 Ces. 


previously dissolved at 110° F., and finally 
add— 


C. Silver nitrate . . 284 gts. 30 g. 
Citric acid , + E5O? sy I 5405, 
Distilled water 240Z. 125 CCS. 


The coating temperature of the above emul- 
sions should be about 95° F. (35° C.). 

If an emulsion suitable for extremely thin, 
flat negatives is required, the addition of a small 
quantity of the chloride of uranium, of nickel 
or of cobalt, to any of the above formule will 
shorten the scale of gradation, but the most satis- 
factory agent is calcium chromate, which must 
be added with caution, as it is extremely ener- 
getic in its action, o-1 per cent, reducing the 
scale of gradation by about one-third. 

For matt surface papers the quantity of gela- 
tine should be reduced so as to make an 8 per 


Emulsions for Development 


cent. solution. More satisfactory matt emul- 
sions can be obtained by incorporating with the 
emulsion 10 per cent. of fine rice starch. The 
necessary quantity of starch should be rubbed 
into a cream with a little water and a small 
quantity of gelatine, taken from the emulsion 
itself, and the whole should be heated to 160° F. 
(71° C.) for an hour and then added to the 
emulsion. (See also “‘ Collodion Emulsion.’’) 


EMULSIONS FOR DEVELOPMENT 
These may be divided into those for positive 
work and those for negative work. 


POSITIVE EMULSIONS 
Positive emulsions may again be subdivided 
into chloride and bromide emulsions, the former 
including chloro-bromide also, and such as are 
Suitable for gaslight papers and plates. 


Chloride Emulsion (Eder) 
A. Sodium chloride . 288 gts. 308. 
or Ammonium chloride 264 ,, 27°5,, 
Hard gelatine . -984y ,, 40,, 
Distilled water 5123 Oe 
Hydrochloricacid . 
B. Silver nitrate . 


400 ccs. 
5 drops 10 drops 
- 576 grs, 60 g. 


Distilled water ee LOO: CLS: 
C. Hard gelatine . = 354 Bis, 40-2, 
Distilled water  IWO%s « Somes, 


Dissolve C by heating to 120° F. (nearly 49° C.), 
and add B at the same temperature; then add 
A, also at 120° F., and allow to stand at this 
temperature for ten minutes; then rapidly cool 
and set. This emulsion yields a satisfactory 
gaslight paper or plate, which readily gives 
warm tones. If the hydrochloric acid is omitted, 
and 240 gts. or 25 g. of citric acid is added, very 
warm tones, from yellow to reddish brown, are 
more easily obtained. If the above emulsion is 
cooled down to 95° F. (35° C.) immediately after 
mixing, and 60 minims or 6 ccs. of liquor 
ammoniz (-880), and 2 oz. or 100. ccs. of distilled 
water are gradually added with constant stirring, 
a much more rapid emulsion is obtained, which 
gives black tones more readily. 

The great trouble in mixing all chloride and 
chloro-bromide emulsions is the formation of a 
coarse grain, which is reduced by the developer 
without exposure to light. For this reason the 
beginner is advised to modify the above formula 
as follows: Add the whole of the gelatine to 
A and increase the quantity of water to 12 oz. 
or 600 ccs., and add the silver nitrate dry, in 
small quantities at a time, with vigorous stirring. 
When all the silver is added continue stirring 
for fifteen minutes, and then add 8 oz. or 400 ccs. 
of distilled water. As an alternative the emul- 
sion may be set and washed as usual, and then 
the extra quantity of water added. Hither way, 
there is less chance of the occurrence of coarse 
grain, and the results are equally satisfactory. 

There is but little difference in the final result 
whether the sodium or ammonium chloride be 
used; the former gives a little more contrast. 
Much harder working emulsions can be obtained 
by adding to the above quantity of chlorised 
gelatine 1:25 grs. or -o5 g. of pure copper 
chloride ; or greater contrasts may be obtained 
by increasing this still further. 

For some gaslight papers an unwashed emul- 


215 Emulsions for Development 


sion is used, but there is far greater liability to 
the formation of black spots. 


Chloro-bromide Emulsions 

Emulsions containing both bromide and 
chloride of silver are more sensitive than pure 
chloride emulsions, and whilst giving warm tones 
with increased exposure, they give better blacks, 
there being less tendency to greenish tones. The 
ratio of bromide to chloride is a matter of taste, 
but the more chloride the less the gradation, 
and the more bromide the faster the emulsion. 


Wratten’s Formula 
Nelson’s No. 1 gelatine 40 grs. 200 g. 
rinse two or three times in water and add to— 
Distilled water . ian Mt me 856 ccs. 


Dissolve at 125° F. (nearly 52° C.) and add— 
Ammonium bromide 


(neutral) + 110 ha 55 g. 
Sodium chloride ee ees pst 
Hydrochloric acid (10% 

solution) ; » TO vmins. SACS, 


Then add in a fine stream— 

Silver nitrate . 200 gts. 100 g. 
Distilled water . ay owe ney 220 ccs. 
with constant stirring. Digest for ten minutes 

at 150° F. (65°5° C.), and add— 

Hard gelatine . - 175 gts. 87°5 g. 
which has been previously washed and soaked 
in water for half an hour and well drained. 
When the gelatine has melted, set, and wash 
for half an hour with six changes of water, 
drain well and melt, and make the total bulk 
up to 1,750 ccs. by adding water. Finally add— 


Tannin . oz LOSe 8, 
Wellington's Formula 
Potassium bromide 384 grs. 40 g. 


Sodium chloride See oy ee pe agi 
Citric acid : sip POD a, 100 ,, 
Hard gelatine Pas Oy, Ym ra pee 
Distilled water . nek 00.2 2,000 Cre 


Heat to 150° F. (65°5° C.), and add— 
Silver nitrate 960 grs. 100 g. 
Distilled water . oe 2D), OZ3. 1 000 secs: 


heated to 150° F. Digest for ten minutes, and 
pour out into a dish to set. 


Valenta’s Formula 


No. I. = 
Ammonium bromide . 480 grs. 50 g. 
Ammonium chloride . 48 ,, aaa 


Nitric acid : 10 drops 20 drops 

Hard gelatine . 1,675 "ges: 168g: 

Distilled water . OO ee earecs 
Heat to 130° F (54°4° C.), and add— 

Silver nitrate . . 960 grs. 100 g. 

Distilled water . oh OY Otago TS Be ees 


also at the same temperature. Allow to digest 
one hour, and then pour out and set. 
No. II., for greater contrasts :— 
The above formula with— 
Ammonium bromide 50 grs. 592 @ 
Ammonium chloride . 300 ,, Cre top 


Emulsions for Development 


In mixing both the Wellington and Valenta 
formule the same procedure may be adopted 
as for Wratten’s. 

The ratio of the silver haloids in these three 
emulsions is as follows :—Wratten—chloride 1, 
bromide 2'1; Wellington—chloride 1, bromide 
1*7; Valenta No. I.—chloride 1, bromide 8:7; 
Valenta No. II.—chloride 7, bromide 1. Welling- 
ton’s gives very warm tones more easily than the 
others with increased exposures. 


Lantern Plate and Bromide Paper Emulsions 


These may be pure bromide emulsions, but 
it is preferable to use bromo-iodide, as the 
iodide tends to keep the whites free from fog. 
Some commercial bromide papers are also 
chlorobromide emulsions. The following gives 
a very satisfactory but slow emulsion, either 
with or without the iodide. 


Ammonium bromide 672 grs. 70 g. 
Potassium iodide he 8 he aa L°Gr% 
Hard gelatine . ye ea ee 160 3., 
Hydrochloric acid (10% 

solution) . 144 mins, 15 ccs. 
Distilled water . 1) 80 Oza T BORn ee 

Heat to 110° F. (about 43° C.), and add— 

Silver nitrate . 960 grs, 100 g. 
Distilled water . Ap tome 8 5 500 ccs. 


also heated to 110°. Digest at this temperature 
for one hour. If a more rapid paper is required, 
then after digestion cool the emulsion down to 
95° F. (35° C.) and add— 


Liquor ammonize 96 mins. IO ccs. 
Distilled water . * I OZ. 50°: 5, 


then set and allow to stand for twenty-four 
hours. 

For enlarging, when a much more rapid paper 
is required, a slow negative emulsion, such as 
given below, may be used, For coating bromide 
paper the proportion of gelatine should not be 
too high, although this depends upon the sur- 
face required and the method of coating, about 
1:18 or 20 being generally sufficient. For 
matt emulsions, rice starch may be added as 
already advised for gelatino-chloride paper. For 
lantern plates a little more gelatine is required, 
say about 1:14. 


NEGATIVE EMULSIONS 

The manufacture of negative emulsions is by 
no means such an easy matter as positive 
emulsion making, but with care slow emulsions 
of very satisfactory quality can be produced. 
The beginner is not advised to attempt very 
tapid emulsions, as they are extremely difficult. 
There are two principal methods for negative 
emulsion making—the acid or boiling process, 
and the ammonia method. The former will 
give, as a rule, the cleaner plate, but it is not 
possible to obtain so high a speed. With care 
equally clean plates may be obtained by the 
ammonia method and greater speed. The acid 
process will be treated first. 


Slow Emulsion 
Potassium bromide 720 gts. eee 


Potassium iodide 5 eee Dire ae 
Nelson’s No. 1 gelatine 317 ,, 5 ee 
Hydrochloric acid. 19h, TCS 
Distilled water . : rrvoz, 550 ccs, 


216 Emulsions for Development 


Heat to 120° F. (nearly 49° C.), and add slowly 
with constant stirring— 


Silver nitrate 960 gts, 100 g. 
Distilled water . * It OZ. 550 ccs, 


also heated to 120° F. Digest in a water bath 
at boiling point for half an hour, and then add— 


Hard gelatine . 1,200 grs, 125 g. 


which should have been well washed in water, 
soaked for half an hour, and drained for half an 
hour, Cool the emulsion, and set. This should 
give an emulsion of about 25 H. and D. 

An emulsion of about double the rapidity, and 
giving somewhat greater contrast can be obtained 
by cooling the above emulsion down to 95° F. 
(35° C.) and adding— 


Liquor ammonie (880) 72 mins. 7°5 ccs, 
Distilled water . ; T° oz, 50 ~ 


and stirring well for about fifteen minutes, then 
setting and allowing to stand for twenty-four 
hours. 

Rapid Emulsion 


Potassium bromide . 1,200 grs. 125 g. 
Potassium iodide <. eeoees pe Pate 
Hard gelatine . «i, wltceted 50 ,, 
Distilled water . oh Or ee 500 ccs. 


Heat to 140° F. (60° C.) and add in a fine stream 
with constant stirring— 
Silver nitrate ..960 gts, 7 1G0e, 
Distilled water . .@ J Of ase ge see 


also heated to 140° F. Digest in a water bath 
at boiling point for forty-five minutes, and 
then add— 

Hard gelatine é - .480 grs,. 49 ¢: 
Distilled water . + eS OR BOG RCES: 
The gelatine should be well washed in two or 
three changes of water, drained, and then dis- 
solved in the distilled water at 110° F. (43-3° C.). 
This should give plates of from 150 to 180 H. 
and D., which are rather soft working but clean. 
Greater contrasts can be obtained by adding 
ammonia as suggested for the slow emulsion. 

Slow Ammonia Emulsion 
Ammonium bromide. 816 grs. 85 g. 


Potassium iodide eG eas 3 ous 
Hard gelatine ay 3Q2 tia TAS igs 
Distilled water . + 20°02, — 1,000 ‘ccs. 


Heat to 110° F. (43°3° C.), and add, with con- 
stant stirring— 
Silver nitrate : 960 gts. 100 g. 
Liquor ammonize (-880) q.s. q.s. 
Distilled water . 6 oz. 300 ccs, 


at a temperature of about 70° F. (21° C.). The 
silver should be thoroughly dissolved and 
enough ammonia added to redissolve the pre- 
cipitate first formed. The exact quantity will, 
of course, depend upon the strength of the 
ammonia, but about 65 or 70 ccs. can be added 
at first, and then further additions made very 
cautiously, stirring well, till quite a clear solution 
is formed. The temperature rises to about 
go° F. (32:2° C.), so that it is advisable to cool 
this silver solution down by standing the vessel 
in cold water for a short time. As soon as the 
emulsion is mixed, the vessel should be placed 


aS ae 


Emulsions for Development 217 


in cold water, running water for preference, 
and the emulsion well stirred till quite thick 
and then put away in cold water to set. If 
allowed to stand for about sixteen hours before 
washing, this should give a clean working plate 
of about 30 to 50 H. & D., which will give great 
contrasts and wide latitude of exposure. 


Medium Rapidity Ammonia Emulsion 


Ammonium bromide. 864 grs. 90 g. 
Potassium iodide ete ee 5 rere. 
Soft gelatine . yy OOrk BO 4, 
Hard gelatine . BARON y, so 7, 
Distilled water . 20 0Z. 1,000 ccs. 


Heat to 120° F, (nearly 49° C.), and add, with 
constant stirring— 
Silver nitrate . 960 grs. 100 g. 
Liquor ammoniz (-880) q.s. q.s. 
Distilled water . : 6 oz. 300 ccs. 


at a temperature of 80° F. (nearly 27° C.). This 
solution should be made as before described. 
When mixed, the emulsion should be digested 
in a water bath at a temperature of 120° F. for 
half an hour, and then— 


Hard gelatine . 480 grs. 50 g. 


which has been well washed but not soaked, 
added. Cool down gradually and allow to stand 
for sixteen hours before washing. ‘This should 
give plates of from 100 to 120 H. & D. 


Rapid Ammonia Emulsion 


Ammonium bromide. 1,152 grs. 120 g. 
Potassium iodide =e ema Bh. 


Soft gelatine . LA ON il, ee 
Hard gelatine . edo 33 Fe 
Alcohol : ; 2 OZ 100 ccs, 
Distilled water . fs te 900 ,, 


Heat to 130° F. (54:4° C.), and add— 
Silver nitrate 960 grs, 100 g. 
Distilled water . ; 6 oz. 300 ,, 
Liquor ammoniz (*880)  q.s. q.s. 


at a temperature of 75° F. (nearly 24° C.). Digest 
in a water bath at 120° F. (nearly 49° C.) for 
one hour, and then add— 


Hard gelatine (well 
washed only) . 1,680 grs. 75 Se 
Cool the emulsion and pour out into flat dishes ; 
allow to stand for twenty hours. This should 
give plates of from 200 to 225 H. & D. 


There are many little dodges which can be 
learnt only by experience and experiment, but 
the following hints may not be useless. 

In making acid emulsions it is advisable always 
to run the silver into the bromised gelatine in 
a fine stream with continuous stirring. In the 
‘case of ammonia emulsions, it is not so important 
to add the silver in a fine stream, but vigorous 
stirring should be continued all the time. 

If regularity of results is required it is 
important that the water bath should always 
be kept at a constant temperature, and, further, 
that the emulsion should be stirred about every 
five minutes, otherwise the silver bromide may 
settle to the bottom of the vessel and give coarse- 
grained thin-working plates that are absolutely 
useless. It will be noted that distilled water 
as advised in all the formule given in this article ; 


é 


1@ 


Enameline 


this is important, as too often ordinary tap- 
water is contaminated with iron and other 
impurities, which lead to fog or loss of sensitive- 
ness. It is advisable even to use distilled water 
for washing the gelatine. 

Greater rapidity can always be obtained by 
reducing the quantity of gelatine during the 
mixing, but there is great danger of the forma- 
tion of coarse grain and fog. If the gelatine 
is much reduced it is always advisable to add 
about 10 per cent. of the total bulk of alcohol, 
which not only prevents this but also obviates 
the occurrence of dichroic fog with the ammonia 
method. 

Directions have already been given for setting 
and washing emulsions. When the emulsion 
has been washed enough it should be removed 
from the water and left to drain for about an 
hour, so as to free it from the adherent water 
as much as possible. In fact, it is as well to use 
a clean dry linen cloth, and after the emulsion 
has drained, place it in this and, collecting the 
whole into the form of a bag, squeeze thoroughly. 
The emulsion is then ready for melting and coat- 
ing. 

A test plate should always be coated first. 
Melt the emulsion in a water bath at 120° F. 
(nearly 49° C.), then take out a little and cool 
down to 95° F. (35° C.); coat a plate and put 
away todry. The bulk of the emulsion can now 
be rapidly cooled down again and, when set, 
alcohol containing o-1 per cent. of carbolic acid 
poured over the top to the depth of about half 
an inch, the emulsion being then put away in a 
dark, cool place. If it is to be used soon the 
alcohol may be omitted, but this will keep a 
stock of emulsion in good condition for a week 
or so. 


ENAMEL, CERAMIC (See “‘ Ceramic Process.’’) 


ENAMEL COLLODION § (See 
Enamel.’’) 


ENAMEL SURFACES 

Highly glazed surfaces. Printing papers 
having such surfaces are now obtainable, but 
formerly the worker had to produce the glaze 
himself. Enamel surface papers need carefu 
washing, otherwise — especially in the case of 
collodion paper—they are liable to crack; they 
also need mounting with a quick-drying mount- 
ant, or else the moisture is liable to spoil the 
glaze. Methods of enamelling prints which in 
their normal state have ordinary or matt sur- 
faces, will be found under the heading ‘‘ Enamel- 
ling Prints.” Proper photographic enamels—that 
is, burnt-in photographs upon porcelain, etc.—are 
known as ‘‘ ceramics.”’ (See ‘‘ Ceramic Process.’’) 


ENAMELINE, OR ENAMEL PROCESS (Fr., 
Procédé émail; Ger., Emaitilverfahrung) 

A process originating in the United States, 
by which a copper or zinc plate is coated with 
a solution of fish-glue and ammonium bichro- 
mate, exposed to light under a half-tone nega- 
tive, developed so as to clear away all the 
soluble glue between the dots, and after being 
dried is ‘‘ burnt-in ’’—that is, the plate is held 
over a gas flame until the image turns to a deep 
chocolate-brown, almost black. When cool, the 


** Collodion, 


Enamelling Prints 


plate can be etched, the enamel image resisting 
the etching solution. Gum is sometimes used 
instead of fish-glue. <A suitable formula for the 
fish-glue solution is :— 


Glue ¥ Oz: 500 g. 
Water ‘ Y 6 SOR Cenere tees 
Ammonium bichromate +;; 25 g. 


Add liquor ammoniz (*880) until a golden yellow 
colour is reached. 

Some workers prefer a formula containing 
albumen, and the following will serve :— 


Le Page’s fish-glue 3 OZ. 375 2g 
Water . : BO Le sha OGi ede 
Ammonium bichromate 180 gts. 47 Z 


Whites of 2 eggs 

Beat the egg whites, add to the glue solution, 
beat up again, allow to stand for eight hours 
and then filter through absorbent cotton. 


ENAMELLING PRINTS (Fr., Emaiilure; Ger., 
Emailleiren) 

The process of enamelling prints must not be 
confused with burnishing, and other methods 
of glazing. Enamelling proper with collodion 
gives the highest possible gloss. The method 
described below is suitable for all kinds of prints, 
but particularly for collodion prints: Procure 
some commercial collodion specially made for 
enamelling, or make according to the instructions 
given under “ Collodion, Enamel,” Thoroughly 
clean a glass plate, rub it over with a little warm 
wax or vaseline, polish well with a soft cloth, 
apply a thick coating of the enamel collodion, 
and allow to set thoroughly. Coat the glass 
evenly and out of the way of dust. This coating 
is to be transferred to the face of the print. By 
the aid of gentle heat, make a solution of gela- 
tine in water (20 grs. to I oz.), and slip the collo- 
dionised glass plate film upwards into the warm, 
not hot, gelatine solution; immerse a dried 
print also in the gelatine solution face down- 
wards, allow it to soak, bring glass and print into 
contact, film to film, lift out and squeegee 
thoroughly until no air-bells are left, and then 
set up to dry. -When quite dry cut round the 
edges of the print (through the collodion) with 
a sharp penknife, lift by one corner, and strip 
from the glass. If properly done, the print will 


come away easily, bringing the collodion sur- 


face with it. 

As the collodion (enamel) surface is easily 
dulled if not mounted with a quick-drying 
mountant, it is the practice of some workers to 
back the print before or during enamelling with 
waterproof paper or thin Bristol board, so as 
to permit the use of any mountant. A good 
method is to soak the unmounted print in 
gelatine, squeegee upon the collodion plate, 
and then immediately after, while the print is 
wet, to squeegee waterproof paper or thin Bristol 
board on to the back of the print, using gelatine 
as the adhesive. When the print and mount 
are dry they can be stripped from the glass like 
an unmounted print,.and then be trimmed and 
mounted. 


ENAMELOID (Fr., Enameloid; Ger., Ename- 
loid) 

A dead-black varnish suitable for the inside 

of lens mounts, diaphragms, etc., said to consist 


218 


Endemann’s Process 


of celluloid dissolved in acetone, with the addi- 
tion of vegetable black. 


ENCAUSTIC PASTE (Fr., Colle encaustique ; 
Ger., Enkaustische Kletster) 

Known also as cerate paste; a mixture for 
rubbing on to the surface of prints in order to 
give them a gloss, deepen the shadows, and 
brighten them up generally. The gloss obtain- 
able is very pleasing, but not so high as that 
obtained by burnishing or enamelling. It is 
patticularly suitable for matt bromide and 
platinotype prints, and at one time was widely 
used for prints on albumen paper. In its sim- 
plest form it consists of 1 part (by weight) 
of ordinary beeswax reduced to a paste with 
four parts of turpentine, the smell of which can 
be masked by substituting 1 part of oil of 
lavender for 1 part of turpentine. The wax 
is soaked in the solvent and then melted gently 
by heat. Another simple paste is that made 
according to Dr. Eder’s formula :— 


White wax oo ROR 500° ccs. 
Dammar varnish - 200 mins. 209 ,, 
Oil of turpentine eo) BOR 500 ,, 


Dissolve by heat and mix well. A more elabor- 
ate mixture, and one widely used, is that made 
according to the Adam Salomon formula :— 


Pure virgin wax - §00 grs, 500 g. 
Gum elemi ; «EO ag ID's 
Benzole . : é 4 oz. 240 ccs. 
Oil of lavender. . ae 36005 
Oil of spike . - . 1 drm, 60.55 


Melt in a hot-water bath, mix thoroughly, and 
strain through muslin; or the gum may be 
dissolved in the solvents and the melted wax 
added after filtration. A small quantity of any 
of the above mixtures is applied to the print by 
means of a small piece of flannel or linen, and 
is then worked into the print by continuous 
rubbing, a polish being obtained finally by rub- 
bing with a clean piece of flannel or a pad of 
clean linen. 

The following mixture was at one time largely 
used for painting with a brush over the shadows 
of a print in order to deepen them; it is not 
encaustic paste proper, but can be used when 
it is not desired to cover the whole of the print :— 


Gum arabic . . + oz. 16°5 g. 
Water P . F Ci: ee 100 ccs, 
Rock candy . as) ECan AS as 
Acetic acid R - Io drops grant 
Alcohol . ‘ Res eee 


ENDEMANN’S PROCESS (Fr., Procédé Ende- 
mann ; Ger., Endemann’s Prozess) 

An aniline printing process, giving a black 
image on a white ground. The paper is sized 
with a solution of 1 oz. of sheet gelatine in 50 oz. 
of water, and sensitised with :— 

A. Sodium chloride 


(common salt) . 480 grs, 846 g. 
Potass. bichromate . 480 ,, 846 ,;, 
Sodium vanadiate . 320 ,, 564 ,, 
Water. . o 20.0% 1,0000c85 

B. Sulphuric acid «i Seah 100 ccs. 


Water . - - SEG, % 
The acid must be introduced gradually into the 
water, and the mixture, when cold, added to A. 


Energiatype 


The paper is floated on the surface of the sensi- 
tiser, and hung up to dry in the dark. It is 
exposed under a negative or tracing in a printing 
frame for about seven minutes, and development 
is carried out by exposing the print to the 
vapour arising from a heated mixture consisting 
of $ oz. of aniline to 25 oz. of water (22 g. in 
1,000 ccs.) for about one minute, which pro- 
duces a brown image. ‘The print is then placed 
in a room filled with steam for about two hours, 
or until the image turns black. To remove the 
green colour that usually remains, wash carefully 
in a solution of liquor ammoniz (-:880) 2 oz., to 
water 12 oz. (166 ccs. liquor ammoniz to 1,000 
ccs, water). 


ENERGIATYPE 

A process (now obsolete) invented and named 
by Robert Hunt about 1851. It has been called 
a ferrotype process, but ferrotypes are now 
understood to be pictures upon a blackened 


tin surface. Good writing paper was prepared 
by washing over with :— 
Succinic acid . ts ETS: 25. g 
Common salt . ‘ fs 2S. 
Gum arabic solution 4 drm 30 ccs 
Water . $ : tof, son"; 


When dry, the paper was sensitised on a solu- 
tion of silver nitrate 60 grs., water 1 oz., and 
dried in the dark. The paper was used in the 
camera as a plate, an exposure of about 30 
seconds being enough for a brightly lighted 
landscape, and six times as long for a portrait. 
The image remained invisible until developed, 
the developer being made in the proportion of 
1 dram of a saturated solution of iron proto- 
sulphate and 3 drams of gum arabic solution. 
The picture was then fixed with ammonia and 
finally well washed. 


ENGINEERING PHOTOGRAPHY 

Most of the technical considerations that apply 
to architectural photography apply equally well 
to engineering subjects. The truth of vertical 
lines must always be preserved by keeping the 


yy 
“LAN 
a a ae 


A. Diagrams showing the Influence of View- 
point in Engineering Photography 


sensitive plate vertical, whether the view of the 
machinery necessitates looking upwards or down- 
wards. In many cases abnormal points of view 
have to be taken, and the camera may have to 
be raised several feet in order to show essential 


219 


Engineering Photography 


features that cannot be seen from any other 
position. One of the most important considera- 
tions in engineering photography must always 
be to show the essential features of the work 
in an effective manner. ‘Technical knowledge, 
or even a slight acquaintance with engin- 
eeting practice, will be exceedingly valuable to 
the photographer who undertakes work of this 


B. Camera Tilted Downwards 


character. The object of the photograph is to 
illustrate the working of the machine; to 
show most plainly its principal working parts 
and the manner in which its object is attained. 
Subject to these considerations, an oblique view 
should always be taken, if possible, in preference 
to a full front or side view. By choosing a 
position that gives a good perspective, the relief 
and projection of the various parts are shown, as 
well as their solidity and their relation to each 
other. In a view taken from the front, the sense 
of relief is largely lost; the machine appears 
flat, its functions are not well shown, and its 
working is much more difficult to follow. The 
diagrams at A show plainly the reasons for this; 
they represent a plan of a machine with the 
camera F placed in different positions. Sharp 
definition throughout is essential. Whenever 
possible, machines should be painted a good 
medium grey or lead colour, this assisting in 
rendering detail effectively throughout, and par- 
ticularly in the shadows and light parts. The 
colour should be quite dull, a glossy surface being 
very undesirable. Bright parts may generally be 
left untouched, as they then look more natural 
than if painted white, as sometimes advocated. 
Paint gives an effect suggesting wood. 

In many subjects difficulties in working may 
present themselves, and require ingenuity com- 
bined with photographic skill to overcome, In 


C. Method of Using Swing-back 


photographing a subject with a long range of dis- 
tances, the following method has been very 
efficient. The subject was some electrically con- 
trolled railway points, and it was very necessary 
to show the mechanism between the rails as 
large as possible. The camera was placed about 
eight or ten feet from the principal part of the 
subject, but signals and other objects five or six 


Engraved Blocks 


hundred feet away were included, and all had to 
be sharply defined. The distance was entirely 
at the top of the picture, and the foreground at 
the bottom, the camera being placed as in 
diagram B. By tilting the camera downwards 
and using the swing-back, as shown at C, sharp- 
ness was obtained throughout by using a medium 
aperture, as the foreground a in the diagram was 
focused at a in the camera, and the distance B 
at b. Previously it was found that with the 
back and front of the camera parallel, f/64 failed 
to render the different planes reasonably sharp. 

In all engineering subjects wide-angle lenses 
should be avoided as much as possible. In photo- 
graphing complete workshops or very large 
pieces of machinery, they may be absolutely 
necessary, but for single machines of small or 
moderate size, a medium-angle or a long-focus 
lens should always be used. 

In many cases machines can be photographed 
out of doors, and this is frequently preferable to 
the lighting in many workshops. 

In most cases, engineers wish to have a clear 
white background for all isolated pieces of 
machinery ; this necessitates painting out the 
background on the plate (see ‘“‘ Blocking Out, 
or Stopping Out’’), unless the work may be 
left to the process-worker’s retoucher. 

Photographing workshops is treated in the 
article “ Factories, Photographing in,” and notes 
on the exposures for these subjects are given 
under the heading ‘‘ Exposure Tables.” 


ENGRAVED BLOCKS 


A term correctly applied to wood-engravings, 
but now commonly used to denote all kinds of 
blocks, whether engraved by hand or pro- 
duced photo-mechanically. 


ENGRAVING (See “ Half-tone 
“* Photo-engraving,” etc.) 


ENGRAVING ON GLASS 


Photographic processes have been employed 
to produce an image on glass as a resist for 
etching by means of hydrofluoric acid. The 
bitumen process is one of the best for the pur- 
pose of forming the resist image. 


ENGRAVINGS, COPYING 

In copying engravings and drawings the only 
difference in working arises from the fact that 
the subject consists of black lines on a white 
ground, a type of subject that is usually con- 
sidered difficult on a gelatine plate, as it is far 
from easy to obtain sufficient contrast with 
ordinary plates. By adopting the following 
method of working little difficulty should be 
experienced in obtaining a negative that will 
give all the contrast required in the print. A 
slow plate of the kind specially prepared for 
this work should be chosen, and it should be 
backed. A fine-grain ordinary, or a process 
plate, will answer well. Correct exposure is 
very important. The following method of 
timing will ensure correct exposure. Place the 
exposure meter flat against the drawing to be 
copied, and note the time required to match the 
standard tint. Using f/16 anda plate of the speed 
of 40 H. and D., one half of the time that a Wynne 
ameter requires, or one fourth of the time required 


Process,” 


220 


Enlarging 


by a Watkins meter to reach the tint, will be 
the correct exposure for copying the same size 
as the original. For other plates or for different 
scales, the proportionate exposures can easily be 
found from these data. Should the lines show 
distinct signs of veiling, development should 
be stopped, and the negative afterwards intensi- 
fied, if necessary. (See also “‘ Copying,” etc.) 

In process work, an engraving on thin, clean 
paper, and with good black lines, without 
printing on the back, may be copied by using 
it as a diapositive. It is placed in contact with 
a sensitised zinc plate and exposed to light for 
a sufficient time. A negative image will be 
developed, but this may be converted into a 
positive one by flowing with a shellac varnish 
containing some colouring matter to make it 
visible. The latter will attach itself to the bare 
zinc lines, whilst that which rests on the sensitive 
colloid film will be dissolved away by treating the 
plate in a bath of weak acid. 

Playertype (which see) is also an easy process 
for copying engravings on to sensitive paper. 


ENLARGING 


The operation of enlarging consists simply 
in taking a print from a negative by means of 
a lens instead of by placing a paper in contact 
with the surface of the negative in the usual 
manner. The essential parts of the apparatus 
required are a holder for the negative from 
which the enlargement is being made; a camera 
body or similar arrangement of which the nega- 
tive holder forms one end, a lens being fitted 
at the other; and a board or easel for holding 
the paper on which the enlargement is being 


| a CC 


Sa 


Principle of Enlarging 


made. The positions of the easel and the lens 
should both be adjustable, so that enlargements 
of any desired size may be made. ‘The illus- 
tration explains the arrangement fully. N is 
the negative, 1 the lens, and Pp the paper. The 
type of lens used for making an enlargement is 
not important, beyond the fact that it ought 
to cover the plate with crisp definition from 
corner to corner with a fairly large aperture. 
If it is mecessary to use a small stop to obtain 
good definition, the exposures required may be 
inconveniently long. Also, a lens of long focus 
should be avoided, especially if very large pic- 
tures are desired from small plates, as the 
apparatus would have to be very long. If the 
focus of the lens is known, the apparatus may 
be set up approximately in position for any 
degree of enlargement by measurement, leaving 
only the fine focusing; it will then be easy to 


Enlarging by Artificial Light 


ascertain what degree of enlargement forms the 
limit of the apparatus. 

The distance A from the centre of the lens to 
the sensitive paper must be equal to the focus 
of the lens multiplied by the degree of enlarge- 
ment, with the focus of the lens added to the 
result. The distance B from the centre of the 
lens to the negative must be the distance A 
divided by the degree of enlargement. The 
distance A bears the same proportion to B as the 
enlargement bears to the original negative. An 
example will render this clear. A lens of 6 in. 
focus is being used to enlarge a 4 in. by 3 in. 
picture up to 12 in. by 9 in. The degree of 
enlargement is three times linear. Three times 
6 in. is 18 in., plus 6 in. brings the distance A up 
to 24 in.; and this distance divided by 3, the 
degree of enlargement, gives 8 in. as the dis- 
tance B. These general principles apply equally 
to all methods of enlarging. Details of making 
enlargements on paper direct, or by means of 
enlarged negatives, are given in later articles, 

It is useful to know the relative exposures for 
different degrees of enlargement, when all the 
conditions are equal. Beginning with the pro- 
duction of a print the same size as the original 
as a basis, and calling the exposure for this 1, 
the relative exposures for other degrees of 
enlargement, using the same stop throughout, 
will be :— 


Degree of 
Enlargement Exposure 
I ss ik I 
14 iis <s 14 
2 ea ne 24 
23 3 
3 aa er 4 
4 - Ms 64 
5 ee ee 9 
6 ¢ ie 


ENLARGING BY ARTIFICIAL LIGHT 
The principal difference between enlarging by 

daylight and by artificial light consists in the 

method of illuminating the negative evenly and 


with sufficient strength to obtain an enlarge- 
ment in areasonable time. A necessary element 
is a condensing lens for collecting the light and 
presenting it in the form of an evenly and 
brilliantly illuminated disc immediately behind 
the negative from which the enlargement is 
being made. The source of light may be an oil 
lamp, a gas flame, or an electric lamp. The 
first-named is the least satisfactory by reason 
of its variable character and comparatively poor 
quality. An incandescent gas burner is one of 
the most satisfactory for general use. At times 
the light is projected in the form of an enlarged 


221 Enlarging by Daylight 


image of the mantle, and a similar difficulty 
may arise with an incandescent electric lamp. 
This may be entirely obviated by interposing a 
sheet of ground glass between the light and the 
condenser, as near the laiter as possible. Other 
methods of lighting the negative are sometimes 
adopted, but in practice they are far from 
satisfactory. The diameter of the condensing 
lens must be fully equal to the diagonal of the 
plate that is being used—for example, 54 in. 
or 54 in. for a quarter-plate; but there is no 
advantage in any size in excess of this. The 
usual arrangement is to enclose the light in an 
iron casing, one end of which holds the condenser. 
By this method the light is excluded from the 
room, so that the paper can be handled freely, 
and the enlargements developed without any 
risk of fogging, excepting when an exposure is 
being made. As close to the condenser as 
possible there is a carrier for holding the nega- 
tive; this carrier forms the back of a camera 
body, the opposite end holding the lens for pro- 
jecting the image. Beyond the lens an easel 
or board is required for holding the sensitive 
paper, and, as the distance between this board 
and the lens, and between the lens and the nega- 
tive, must be varied according to the degree of 
enlargement, a method of extending the camera 
body, and one for sliding the easel, have to be 
provided. The easel should slide on guides, as 
it is imperative that it should be quite parallel 
with the negative. The arrangement will be 
more easily understood from the illustration, m 
which G is an incandescent gaslight, c the con- 
denser, N the negative, 1 the lens, and P the 
paper on which the image is received. 

The exposure will depend on the negative, the 
paper, and the degree of enlargement. In 
enlarging from quarter to whole-plate by incan- 
descent gas, with lens aperture f/8, the exposure 
will vary from ten seconds for a thin negative 
up to forty for a strong one, using a commercial 
bromide paper. A test exposure on a small 
piece of paper should always be made before 
making the enlarged print. The test piece 
should include the strongest part of the nega- 
tive. 

Any negative that will give a good contact 
print on bromide paper will yield a good enlarge- 
ment by incandescent gaslight with a con- 
densing lens for concentrating the light. 


ENLARGING BY DAYLIGHT 

This method gives greater opportunity for 
varied methods of working to suit the conditions. 
of different photographers than does enlarging. 
by artificial light. The apparatus and the man- 
ner of using it may range from the simple and 
inexpensive fixed-focus enlarger up to a per- 
manently arranged apparatus in which the dark- 
room itself forms the camera in which the enlarge- 
ment is made. The general principle is illus- 
trated in the article “‘ Enlarging.’ It is the: 
method of adapting that principle to the require- 
ments of the worker that varies. The most 
simple is the fixed-focus enlarger, a piece of 
apparatus in the form of a double box, which 
allows one degree of enlargement only. This is. 
an inherent disadvantage of a fixed-focus 
instrument, but it has the advantage of great 
convenience; it is ready for use at a moment’s. 


Enlarging by Daylight 


notice, without any focusing or arranging. The 
negative is placed film downwards at N (see 
illustration A), the paper put in position at P; 
the apparatus taken out of doors, so that the 
light from the sky overhead falls directly on 


A, Diagram of Fixed-focus Daylight Enlarger 


the negative, and the exposure made by operating 
the shutter that closes thelensy. This apparatus 
gives enlargements of one uniform size only, 
this size varying with its construction and the 
size of the negatives for which it is intended, 

A second form of apparatus is an enlarging 
‘ camera (which see). Illustration B shows how 
the apparatus is used: N is the negative, 1, the 
lens, and P the sensitive paper. 

A third arrangement is one that is frequently 
adopted by those who do much enlarging, and 
who wish to have a much larger range in size 
than that which can be obtained in an enlarging 
camera. The dark-room, or a room that can 
be darkened by closing the window with a 
specially-made shutter, becomes the enlarging 
camera. The camera in which the original 
negative was taken, and an enlarging easel, are 


fr | | 
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practically all the apparatus that is required. 
The window of the room is closed by a shutter 
(see illustration C), in which is a small opening 
a little larger than the negative. Outside the 
shutter a reflector of white card or a dull white 


222 


Enlarging Camera 


painted board is fixed so as to reflect the light 
from the sky through the negative. Inside the 
toom the camera is supported on a table 
opposite the opening in the shutter. The 
negative N is placed in the camera back, film 


U / 
MEE SSS 


) ae / 
y a ty YWGN 
y i y AM 
A Pi DN 
C. Showing use of Reflector in Daylight 
Enlarging 


towards the lens, and a focusing cloth wrapped 
round the camera back so as to prevent any 
light leaking into the room. On the table an 
easel holding the paper P is arranged to slide 
in guides, the image being projected by the 
lens 1, in the usual manner, Pas 
A difficulty in daylight enlarging is the ever 
vary:ng character of the light. A test should 
always be made by a meter immediately before 
making an exposure. It is only by this method, 
and small test pieces as described in “* Enlarging 
by Artificial Light,” that correct exposures can 
be secured. Any negative that will give a good 
contact print on bromide paper will yield an 
equally satisfactory enlargement by daylight. 


ENLARGING CAMERA (Fr., Chambre d’ agran- 
dissement ; Ger., Vergrésserungskamera) 

A camera for making enlarged photographs on 
bromide paper, or enlarged negatives, from 
smaller negatives or positives. It consists 
essentially of a carrier or holder for the negative, 
a dark-slide or frame for the bromide paper, and, 
between these, a support for the lens, the whole 
being covered in except the end at which the 
negative is placed. In a fixed-focus enlarging 
camera, of which A is a typical example, the 
distance between negative, lens, and dark-slide 
cannot be varied, and only one size of enlarge- 
ment is possible; but in other forms of appara- 


i i 

A. F 

tus, as in B, there is provision for altering these 
distances to obtain enlargements of different 
sizes. The cameras just considered do not re- 


quire the room to be darkened if used indoors ; 
they may, if preferred, be used outdoors. The 


Enlarging Easel 223 


non-portable enlarging camera, however, as 


generally used in trade establishments, is placed 
close against a window, from which all actinic 
light except that illuminating the negative is 
blocked out. With this form of enlarger an 


easel is usually employed instead of a dark-slide. 
Any ordinary camera may be used in this way 
if a suitable holder or carrier is made for the 
negative; or the negative may be placed in the 
dark-slide, this being inserted in the camera with 
both shutters drawn, to serve as a carrier. To 
obtain a uniform light, a white card or reflector 
is fixed outside the window at an angle of 45°. 
An alternative is to use a sheet of ground glass, 
or to paste white tissue paper over the opening 
which admits light ; when this is done the nega- 
tive should be a few inches distant from the 
opening instead of close against it. Various 
lamps are obtainable to fit behind the negative 
carrier of daylight enlargers, thus enabling them 
to be used by artificial light. 


ENLARGING EASEL (See “‘ Easel, Enlarging.’’) 


ENLARGING LANTERN  (Fr., Lanterne 
@agrandissement ; Ger., Vergrdsserungs- 
apparat) 

A lantern used in enlarging by artificial light, 
to project a magnified image of the negative on 
the bromide paper. It consists of a body carry- 
ing the illuminant, a condenser to concentrate 
the light on the negative and cause it to pass out 
from the latter in a converging cone, and a pro- 
jecting lens or objective to receive the cone of 
light from the condenser and to form the enlarged 
image. A illustrates the optical system of the 
enlarging lantern, A being the illuminant, B the 
condenser, C the negative, D the objective, and 
& the projected image. The condenser must be 


A. Optical System of Enlarging Lantern 


of sufficient size to illuminate the whole of the 
negative, or part of the image will be cut off 
towards the margins of the enlargement; on the 
other hand, there is no advantage in having too 
large a condenser, but rather the reverse, as 
light is wasted. For a quarter-plate negative, a 


Enlarging Lantern 


54-in. diameter condenser is required; for a 
half-plate, one of 84 in. diameter; and for a 
whole-plate, one of 11 in. diameter. ‘The con- 
denser has nothing whatever to do with the size 


B. Enlarging Lantern with Rack and 
Pinion Adjustments 


of the enlargement; this depends, other things 
being equal, entirely on the distance of the 
bromide paper from the projecting lens or objec- 
tive. The objective should. be capable of 
covering the size of negative to be enlarged, and 
of sufficient diameter and aperture to pass the 
whole of the beam of light proceeding from the 
condenser. The lens used in making the nega- 


tive is usually suitable for enlarging, the best 
possible projection lens being probably a good 
anastigmat. There are numerous illuminants 
employed for enlarging, as oil, acetylene, incan- 
descent gas, incandescent spirit, limelight, the 
electric arc, the Nernst lamp, etc. Of these, 
limelight and the electric arc are the most 
efficient with regard to illumination, owing to 
their approximating more nearly to a small 


D. Lantern Body Attached to Camera 


point of light; but from the point of view of 
general convenience and utility, incandescent 
gas is perhaps the favourite. The proper 
adjustment of the illuminant is of importance, 
or the enlargement will be unevenly lit. The 


Enlarging Negatives 


correct procedure is to place the negative in the 
carrier and to focus roughly to the required size, 
approximately centring the light and bringing it 
to that distance from the condenser which seems 
to give the best and most even illumination. The 
negative is then removed, and the illuminant 
moved back till a dark ring appears round the 
disc of light on the easel. The illuminant is 
now carefully centred till the ring is equal all 
round, and is then pushed toward the condenser 


FE. Ellipsoid Enlarging Lantern 


till the ring disappears and a perfectly even 
lighting is secured, the negative being finally 
re-inserted and sharply focused. Any after 
alteration in the size of the enlargement will 
require a fresh adjustment of the illuminant. 
B shows a typical high-class enlarging lantern 
which has rack and pinion adjustments through- 
out, including provision for moving the lantern 
body, the a pao and the objective. The 
negative carrier is furnished with rising, falling, 
and swing movements, and a rise or fall is also 
permissible with the lens. C illustrates a cheaper 
enlarging lantern, of simple yet efficient con- 
struction; while D represents a useful type 
dispensing with the extension bellows and pro- 
jection lens, and intended to take an ordinary 
camera in front. In another form of enlarging 
lantern, known as the ellipsoid enlarger, no con- 
denser is used, the negative being lit by reflected 
light from a curved opal reflector; these 
enlargers are made either for use with the 
worker’s own camera, or with a bellows and pro- 
jection lens, as in E, where a pair of inverted 


incandescent gas burners form the illuminant. » 


ENLARGING NEGATIVES 


In order to make a large negative from a small 
one, two operations are necessary. A trans- 
parent positive must be made from the original 
negative, and from that a new negative can be 
made by enlarging to any desired size. The 
character of the transparent positive is of the 
greatest importance in determining the character 
and quality of the new negative. The extreme 
shadows or densest parts should be moderately 
strong, but such an exposure should be given 
that the highest light is veiled. No part should 
be quite clear, and the transparency should be 
dull rather than brilliant. The best method for 
making the transparency is by contact printing 
by artificial light on a rapid plate, thus securing 
the truest reproduction of the gradation of the 
original. For the same reason—the desirability 
of reproducing all the gradations as correctly 
as possible—the enlarged negative should par- 
take of the same character ; the deepest shadow 


224 


Enlarging on Paper 


should be veiled, otherwise there will be a dis- 
tinct loss of tone values. The method of working 
is given under “Enlarging by Daylight” and 
“* Enlarging by Artificial Light,” excepting that 
the transparent positive is placed in the position 
there described for the negative and a plate in 
the position given for the sensitive paper. Backed 
plates should be used for making the transparency 
and the enlarged negative, and the film side 
should be towards the lens in each case. Film 
towards film is the rule, as in printing. An 
exception to this is when a reversed negative is 
required for the carbon process. In that case 
the transparent positive is reversed in the carrier, 
the glass side being turned towards the lens. 

Enlarged Paper Negatives.—Enlarged nega- 
tives may be made on bromide paper from lan- 
tern slides or other transparencies, the bromide 
paper after exposure being treated with a weak 
bichromate solution, as described under the 
heading “* Sterry’s Process,” in order to obviate 
harsh results. By the W. Coats method, an 
enlargement is made on rapid smooth bromide 
paper, the exposure being short so as to keep 
the shadows clear; amidol is used as the 
developer and the print is washed for two 
minutes; the unfixed print is then toned in the 
following bath, in which it should remain for 
seven minutes, at least :— 


A. Pot. ferricyanide . 40 grs, 8 g. 
Glacial aceticacid . 4 oz. 50 ccs 
Water . ‘ 4 Oe T 000) o2 

B. Uranium nitrate . 4o rs. 8 g. 
Glacial acetic acid . 4 oz. 50 ccs 
Water . . + 13 1,000 ,, 


Take equal parts of each just before use. The 
solutions keep well separate, but not when 
mixed. When toning is complete, the print is 
well washed and immersed for one minute in a 
solution of 20 grs. (4 g.) of ammonium sulpho- 
cyanide in 20 oz. (1,000 ccs.) of water. The 
print is washed again for two minutes and then 
exposed to 4} in. of magnesium ribbon burning 
at a distance of 12 in. from it. The print is 
next rinsed and redeveloped in the original 
amidol developer, fixed in “ hypo,” and washed. 
A metol-hydroquinone developer has been sug- 
gested in place of the amidol. 

An important point which must not be over- 
looked in all enlarging processes is the increase 
in contrast in the resultant print or plate. This 
is caused by the scattering of the light by the 
silver grains of the negative, which practically 
act as points from which the light spreads or 
scatters out in fan-shaped bundles, and there- 
fore does not reach the lens. This may be over- 
come by placing the negative film side next to 
a sheet of fine matt opal glass, 


ENLARGING ON PAPER ° 

The most simple and satisfactory method of 
enlarging is to produce an enlarged print on 
paper direct from the original negative. It is 
not only the most simple method, but it ensures 
the truest reproduction of the gradation and 
quality of the negative. There is only one print- 
ing medium sufficiently rapid for direct enlarg- 
ing—at least, by artificial light—and that is 
paper coated with a silver bromide emulsion. 
(See “ Bromide Paper.”) Enlarged prints pro- 


Enlarging by Stripping 


duced on this paper are in every respect equal 
to contact prints from the same negative, and 
the development, fixing, and after processes 
are precisely similar. The only difference is in 
the methods of obtaining the print. These are 
given under “‘ Enlarging by Artificial Light’ and 
“Enlarging by Daylight.” 


ENLARGING BY STRIPPING 

A process of stripping a film from an ordinary 
unvatnished negative, enlarging it, and attaching 
it to a larger glass; the process dates from 1882. 
The following enlarging mixture is required :— 


Hydrofluoric acid .1 drm. 31 ccs, 
Citric acid 4 oz. reo), 
Glycerine . = ere “Cite: LY eee 
Acetic acid F pie OZ 195°) 53 
Water ‘ 3 oo ae 1,000, 


The hydrofluoric acid needs careful handling. 
The negative is placed in the solution and the 
film will gradually become released from the 
glass and at the same time be enlarged. If 
necessary, the film can be assisted to leave the 
glass by means of a camel-hair brush. It is 
next carefully rinsed in water and floated upon, 
and squeegeed into contact with, a cleaned glass 
of the required size. In this way a quarter 
late may be expanded to fill a half plate, and 
arger sizes in proportion. When in contact 
with the new and larger glass it must be allowed 
to dry naturally. As may be expected, films 
enlarged in this manner give slightly thinner 
results, and a rather dense original is therefore 
advisable. Films may be stripped from nega- 
tives without any enlargement. (See under the 
heading, “Film Stripping.) Theolder the nega- 
tive the more difficult it is to strip and enlarge. 


ENSEMBLE (Fr.) 
The arranging or grouping of several figures 
or of the constituent parts of a picture. 


ENVELOPE SYSTEM (See “‘ Daylight Chang- 
ing.’’) 
EOSINE (Fr., Eosine ; Ger., Eosin) 

Synonym, yellowish eosin or eosine. C,H, 
(CO C,H Br, OK), O. Molecular weight, 708. 
Soluble in water, alcohol, and ether. It usually 
occurs as a red powder. The sensitising power 
of eosine lies between E and Din the green and 
yellow green, but does not reach the D line. 

METHYLERYTHRINE is the methylic ether and 
primrose, or erythrine is the ethylic ether of 
tetrabromofluorescein. 

The eosines are a somewhat large class of 
dyes known generally as the phthalein group, 
and derived from triphenylmethane. The first 
dye of this group is :— 

FLUORESCEIN (Fr., Fluorescine ; Ger, Fiuore- 

scein) 

Solubilities, insoluble in water, soluble in 
alcohol. A brick red powder of little photo- 
graphic interest except as the starting-point of 
other dyes. Its sodium salt is called :— 

URANIN (Fr., Uvanine ; Ger., Uranin) 

Coo Hi, O; Nag. Solubilities, soluble in water, 
alcohol, and ether. A brownish red powder 
which is sometimes used for making yellow 
screens or dark-room filters. 

15 


225 


Erythrosine 


Assuming the formula for fluorescein to be 
C, H, (CO C, H; OH), O, the hydrogen atoms of 
the resorcinol group in brackets can be replaced 
by the halogens chlorine Cl, bromine Br, and 
iodine I., and according to the number of sub- 
stitutions there are formed monobromofluore- 
scein, dibromofluorescein, known as eosine extra 
yellow, and _ tetrabromofluorescein yellowish 
eosin; these are used for sensitising collodion 
emulsion for yellow-green; and the mono- 
bromofluorescein is an excellent green sensitiser. 
Their action on gelatine plates is less satisfactory 
than that of erythrosine, All these dyes have 
a greenish fluorescence in solution, and form salts 
when mixed with silver nitrate which are prac- 
tically insoluble in water. 

In process work, eosine is often used for dyeing 
the fish-glue image in the enameline process ; 
but methyl violet is more commonly employed, 
and is preferred because it shows up the image 
in greater contrast. 


EPHEMERAL PHOTOGRAPH 

A kind of phosphorescent photograph, pro- 
duced by one of the many processes introduced 
by the late W. B. Woodbury. Largely quoting 
from his own words, the process is simple, and 
the same piece of sensitised paper may be used 
over and over again, while at the same time 
always retaining its sensibility. The material is 
the phosphorescent powder, calcium sulphide, 
obtained by calcining oyster-shells and treating 
with sulphur. <A sheet of paper is coated with 
this by covering with gum or varnish, and dust- 
ing the powder overit. If this paper is exposed 
for a few seconds to light under a positive trans- 
parency and then removed to a dark-room, a 
luminous positive will be seen, lasting a longer 
or shorter time, according to the exposure given. 
Woodbury also produced luminous portraits and 
views by the dusting-on process, substituting 
the powder named for plumbago. (See also 
‘Luminous Photographs.’’) 


EPSOM SALTS 

The common name for magnesium sulphate, 
which has been advocated as a preventive of 
frilling ; the dry plate previous to development 
is soaked in a saturated solution of the salts. 
Also, a saturated solution of the salts made 
with beer and a little gum water is used for 
‘frosting ’’ studio and other plain glass windows. 


EQUIVALENT FOCUS (See “ Focal Length.’’) 


ERYTHROSINE (Fr., Evythrosine; Ger., Ery- 
throsin) 

Synonyms, erythrosin, bluish eosin, iodoeosin. 
C, H, (COC, HI, ONa), O. Molecular weight, 660. 
Soluble in water, alcohol and ether. It is a 
bluish red powder which, when pure, gives no 
fluorescence in aqueous solution, and but slight 
fluorescence in alcoholic. It forms an insoluble 
silver salt, erythrosinate, or tetraiodofluorescin- 
ate of silver, which is used with collodion emul- 
sion for colour sensitising. Erythrosine is the 
most energetic yellow-green and yellow sensitiser 
for gelatine emulsions, its action extending from 
# to beyond D; it leaves, however, a character- 
istic minimum or lack of sensitiveness in the 
blue-green between b and F. It may be added 


Essence of Jargonelle 


to the emulsion at the time of mixing, in which 
case 0-2 per cent. should be added to the bro- 
mised gelatine before adding the silver nitrate, 
or it may be added the last thing before coating, 
or it may be applied in the form of a bath to 
the finished and dried plate; this method gives 


the greatest colour-sensitising effect, The plate 
should be soaked for two minutes in :— 
Liquor ammonize . 96 mins, IO ccs. 
Distilled water to 20 OZ. T.06G"",; 
drained and immersed in— 
Erythrosine -96 grs. I g. 
Liquor ammonize . 192 mins, 20 ccs, 
Distilled water to 20 OZ. T5000). 5 


and then well dried in the dark. A considerable 
saving of time is effected in the drying if one 
third of the quantity of water in the above 
formula be replaced by alcohol or acetone. 

Erythrosine M is the sodium or potassium salt 
of tetrabromofluorescein as above; erythrosine 
G is a similar salt of diiodofluorescein. 


ESSENCE OF JARGONELLE (See “ Amyl 
Acetate.’’) 


ETCHING (Ftr., Morsure ; Ger., Aetzung) 


The incision of metals by means of acids or 
other corrosive fluids, as distinguished from 
engraving, which implies incision by cutting 
with a graver. Etching may be of two kinds: 
(1) The older form consists in spreading an acid- 
resisting coating, or ‘‘ ground,” on the metal 
plate and scratching through it by means of 
sharp points so as to lay bare the metal. This 
is the process used by artist etchers, from 
Rembrandt down to the present-day workers. 
(2) The other and more modern method, in 
which photographic processes play so large a 
part, consists in forming an image on the plate 
in ink, varnish, or other suitable acid-resisting 
medium, and then etching away the bare parts of 
the metal. The image may be applied by draw- 
ing direct on the plate, by transfer from a greasy 
ink image on paper, or by photography with a 
sensitive film. The last-mentioned method, now 
by far the most common, is called photo-etching. 
The methods of forming the image on the metal 
are treated under various headings—for example, 
‘‘ Albumen Process,”’ “‘ Fish-glue Process,” “‘ En- 
ameline,”’ ‘‘Bitumen,’’ etc.—and the etching 
inks, solutions, metals, etc., are also separately 
described. Etching may be either in relief or in- 
taglio, the former being necessary for typographic 
printing and the latter for copper and steel plate 
printing. There are two divisions—line etching, 
which reproduces lines, stipples, and solid patches 
of colour ; and half-tone etching, which interprets 
the tones of a photograph or painting by means 
of a dot system. Colour etching is merely an 
extension of one or other of these processes. 

Photogravure etching (which see) is different 
in principle. In ordinary etching the sunk 
lines, or spaces between the lines, are practically 
of uniform depth, but in photogravure etching 
the depth is proportionate to the tones, the 
shadows being sunk the deepest into the plate. 


ETCHING BATHS 


This term is applied to the etching solutions 
and also to the troughs and trays used for 


226 


Etching Machines 


holding them. To prevent confusion, the vessels 
themselves are treated in the present article, 
the solutions being described separately in the 
article headed ‘‘ Etching Solutions.” The baths 
are of wood, lined with pitch or gutta percha; 
of slate; or of earthenware; and they are 
generally mounted on rockers, so that the solu- 
tion may be washed to and fro over the plate. 
The ends are covered to prevent the splashing 
of the acid out of the trough. In large shops 
the troughs are mounted on a rocking machine 
driven by motor and worm gearing, this ensuring 
more uniform etching. 


ETCHING INK 


There are numerous formule for etching inks, 
these varying according to the particular branch 
or process of etching for which they are required. 
In America the term is limited to the ink used 
for rolling up the albumen bichromate print 
after exposure as a preliminary to development. 
Excellent commercial inks are obtainable, so 
that it does not pay to make one’s own ink, 
but it may be useful to know that such an ink 
usually consists of beeswax, soap, shellac, litho- 
graphic ink, lithographic varnish, and similar 
ingredients well mixed together. Etching ink, 
as usually understood by English workers, may 
also mean “‘ starting ink,’ or soft etching ink, 
and “‘ finishing ink,’’ or hard etching ink. ‘These 
inks can also be purchased ready-prepared. The 
former consists of such ingredients as Russian 
tallow, yellow beeswax, asphaltum, lithographic 
or letterpress printing ink, and thin lithographic 
vatnish. The object of this resist is to form a 
covering for the shoulders of the lines by running 
down the sides when the plate is heated. It is 
usually applied by inking the surface with a 
lithographic leather nap roller. The “ finish- 
ing ink’’ consists of beeswax, resin, asphaltum, 
and lithographic printing ink. It is necessary to 
warm the plate in order to get the ink to “ take,” 
and it is applied by means of a lithographic 
glazed leather roller. 


ETCHING MACHINES 


Since about 1895 etching machines have come 
much into vogue in photo-engraving establish- 
ments. ‘The earliest machine of the kind to be 
brought into commercial use is the Levy Acid 
Blast. (See ‘Acid Blast.) The Axel etching 
machine, invented by Axel Holmstrom, has 
a paddle-wheel working in the bottom of the 
etching trough and throwing the acid against 
the plate, which is placed almost vertically 
against the side of the trough. The Mark 
Smith machine is similar in principle, but 
the plate is placed horizontally over the 
etching trough, and remains stationary. The 
Albert etching machine consists of a horizontal 
trough which has a slow reciprocating motion, 
The plate is laid face up on a platform at the 
bottom of the trough. This platform is lifted 
out of the solution when the lid is raised. This 
lid has on its underside a series of ribs or vanes, 
and it is given a rapid reciprocating motion 
when laid down over the plate, so that the acid 
is put into a state of violent agitation, causing 
the plate to be etched more rapidly than it 
would be in a rocking trough. The “ Holt” 
etching machine has a trough and a lifting plat- 


ee a, ee ae 


—s 


Etching Metals 


form similar to the Albert machine, but the 
solution is agitated by means of a rotating disc, 
on the underside of which are vanes for churning 
up the solution. The ‘‘ Danesi’’? machine rains 
the acid down on the plate from a trough above, 
into which the acid is pumped from the etching 
trough below. 

Various other forms of etching machines have 
been proposed and patented, but the foregoing 
have come into regular use. 


ETCHING METALS 

The metals used for etching are generally 
zinc, copper, brass, and steel. Zinc is mostly 
used for line work, copper for half-tone and 
photogravure, brass for half-tone and for book- 
binders’ blocking plates, and steel for die 
printing. Carefully smelted and rolled metal 
is used, and the sheets are highly planished and 
polished. For line and half-tone the plates are 
usually from 14 to 16 B.W.G. (-083 in. to :065 in.) 
ri thickness, and the metal is purchased ready 
or use. 


ETCHING SOLUTIONS 

For zine etching nitric acid is invariably 
used, the strength varying from 1 to 20 per 
cent. according to the stage of the etching and 
the nature of the work. The bath has to be 
constantly rocked whilst the plate is being 
etched. A “still” etching solution, which does 
not require rocking, consists of :— 


Nitric acid . 130 parts 
Water ; ; . POU Ly ecg 
Sal ammoniac : ee wh 
Pyroligneous acid (wood 


vinegar) . ; > hog eo 


The bath should stand two or three weeks after 
mixing. Another bath for zinc which need not 
be rocked is :— 


Sulphuric acid . 7 6 parts 
Potassium nitrate ‘ ea aie 
Water * : gr Paes, 


Dissolve the potassium nitrate in water, and then 
gradually add the acid. Dilute with water till 
bubbling ceases. 

For etching an enamel film without “ burning- 
in’ the image, the following bath is recom- 
mended :— 

Alcohol (40 %) 400 parts 
Nitric acid OTR Oh Py Pee 


For half-tone copper etching, iron perchloride 
is dissolved in water until the solution registers 
from 35° to 40° on the Beaumé hydrometer 
(up to 1°36 sp. gr.). About 14 lb. perchloride 
to 1 pint of water will bring the solution to the 
required strength. The solution is improved 
for immediate use by adding 4 pint of an old 
bath to every quart of new. Rocking the bath 
makes the etching proceed more quickly. Heat 
also aids the etching. Sometimes the plate is 
etched face downwards, held in a clamp. 

Brass is also etched with perchloride of iron 
at 35° Beaumé. 

Steel can be etched with ferric perchloride 
at 40° Beaumé, or with a strong solution of 
chromic acid, or with acetic acid five parts, 
fuming nitric acid one part, diluted as may be 
necessary with distilled water. 


227 Euryscope 


The term “etching solution” is also applied 
to the solution of glycerine, with other ingredi- 
ents, such as liquor ammonie, calcium nitrate, 
sodium chloride, etc., used for damping the 
collotype plate. Again, “‘etching’’ is applied 
to the operation of spreading over the litho- 
graphic stone or zinc or aluminium plate a 
slightly acid gum solution, which prepares the 
surface for clean inking and printing, though it 
does not actually etch into perceptible relief. 
Such etching solutions for zinc contain a decoc- 
tion of nutgalls and phosphoric acid, and for 
aluminium phosphoric or hydrofluosilicic and 
other acids. 


ETHER (Fr., Ether sulfurique ; Ger., Aether) 

Synonyms, ethyl oxide, ethylic ether, sulphuric 
ether. C,H,;OC,H;. Molecular weight, 74. 
Solubilities, 1 in 12 water; miscible in all pro- 
portions with alcohol, chloroform, benzole, etc. 
It is a limpid, very light, and volatile transparent 
liquid with characteristic odour and burning, 
sweet taste. It is made by distillation from 
sulphuric acid and alcohol. The vapour being 
very heavy and inflammable, ether should be 
kept in a well-stoppered bottle in a cool place. 
In large quantities it and its vapour are poison- 
ous, the antidotes being an emetic or the use of 
a stomach pump, free supply of fresh air, ammo- 
nia, and artificial respiration. It may be pre- 
pared from either ethyl or methyl alcohol, the 
latter giving the so-called methylated ether 
which can be used for all photographic purposes. 
The specific gravity should be -720. It is used 
for making collodion and varnishes. 

In process work, ether is largely used for 
making collodion and collodion emulsion, the 
kind usually employed being methylated ether, 
sp. gr. -720, washed and redistilled. It is also 
used for washing bitumen to increase its sensi- 
tiveness, and with alcohol as a solvent for 
bitumen in a process for graining the plate by 
reticulation of the film. 


ETHOXY LIMELIGHT 

Limelight produced by raising a spot on a 
cylinder of lime to a state of incandescence by 
means of a non-luminous flame of mixed ether 
vapour and oxygen. The mixture is prepared in 
a saturator (which see). Oxyhydrogen is a cor- 
responding term indicating that a mixture of 
hydrogen and oxygen is burnt. 


ETHYL ALCOHOL (See “ Alcohol.’’) 
ETHYL OXIDE (See “ Ether.’’) 
ETHYLIC ETHER (See “ Ether.’’) 


EURYSCOPE 

Under this name Voigtlander and other 
opticians have issued lenses of the rapid recti- 
linear type, of intensities varying from f/4°5 to 
f/7. Similar lenses were issued by Ross as 
* Universal Symmetricals’”? and by Dallmeyer 
as “‘ Extra Rapid Rectilinears.” The rectilinear 
portrait lens of the latter maker was really a 
eutyscope with an aperture of f/3. Slower forms 
of euryscope for wide-angle work, copying, etc., 
have also been made. ‘Their greatest intensity 
varies from //9 to f/15. 


Evaporating Dish 


EVAPORATING DISH 

In wet collodion photography this is a most 
important utensil for evaporating the silver 
bath when it has become deteriorated by use 
or by impurities. Usually the silver bath is 
boiled to evaporate about half the volume of 
solution, and then made up to strength again 
with distilled water and additional silver nitrate. 
Any alcohol and ether is thus driven off, and 
the iodising salts dissolved out of the collodion 
film are reduced in proportion to the volume of 


Porcelain Evaporating Dish 


the new solution. Amongst English and Con- 
tinental workers the common laboratory form of 
porcelain basin is used, the bottom, outside, 
to which the greatest heat is applied, being left 
unglazed. It is best to embed the basin in a 
sand bath to avoid fracture by the application 
of direct heat. In America stamped enamelled 
iron dishes, called Agate ware, are largely used 
without any apparent drawback, and of late 
many English workers have taken to using cast- 
iron enamelled dishes. A good way of testing 
for faults in the enamel is to fill the enamelled 
vessel with copper sulphate. The acid will 
attack the iron wherever it can reach it through 
the small pores, and little beads of copper are 
deposited in small spots, gradually increasing in 
size until they become plainly visible. Such 
dishes are obviously unsuitable. 


EVERSET SHUTTER (Fr., Obturaieur toujours 
ayvmé, Obturateur automatique; Ger., 
Selbsithatiger Verschluss) 

Any shutter that does not require setting 
before an exposure can be made. An everset 
shutter is an obvious advantage, since an unex- 
pected opportunity of photographing a moving 
object might be lost even in the short time 
occupied in setting the shutter. 


EXCITING 
The old and practically obsolete name for 
sensitising. 


EXPANSION OF PAPER 


EXPANSION, REDUCING DENSITY BY 
(See ‘* Reduction, Mechanical.’’) 


EXPLOSIVE POWDER 
Powders.’’) 


EXPOSING, METHODS OF 

The usual methods of exposing dry plates 
in a camera are by means of a cap or shutter. 
The cap method was the original one, and 
although it is considered old-fashioned it still 
has advantages. In landscape work the cap 
may be made to serve as a.lens shade by holding 
it above the front of the lens during exposure. 
The correct way to uncap a lens is to imagine 


(See “ Paper.’’) 


(See “* Flashlight 


228 


’ Exposure 


that itis hinged to the top of the lens hood. The 
cap is loosened by twisting and the lower edge 
raised until it is clear of the lens, and replaced 
again when exposure is finished; in this way 
the cap not only serves as a lens shade, but, by 
raising and lowering at a suitable speed, one can 
give more exposure to the foreground than the 
sky, and at times obtain clouds on the negative 
which would be missing on account of over 
exposure if the sky had the same amount of 
exposure as the landscape. 

By the judicious use of a cap one may picture 
a busy street as being empty, and such a method 
is sometimes handy when one desires a photo- 
graph of a building in a busy street without 
showing the traffic. The lens in such a case is 
stopped down to its very smallest extent, the 
smaller the better, so as to require a very long 
exposure, the longer the better; exposure is 
then made by a series of very brief exposures 
with a cap. Assuming, for example, that an 
exposure of one minute is considered to be 
necessary, the plate is exposed for two seconds 
and the cap carefully replaced, another two 
seconds is given, and so on until the plate is 
considered to be fully exposed. The brief 
exposures will not be enough to picture moving 
objects, and only those which have remained 
still during the greater part of the minute will 
show when the plate is developed. 

Shutter exposures are invaluable in cases of 
portraiture, and of course absolutely necessary 
for instantaneous work, as the quickest “ off 
and on’”’ cap exposure possible is estimated to 
be one-fifth of a second, but in the majority of 
cases it is nearer half, or even a whole, second. 
Silent-working shutters, preferably those which 
work inside the camera, are the best for por- 
traiture, as those which work noisily and outside 
the camera are apt to startle the sitter, or other- 
wise attract attention at the wrong time. Chil- 
dren, for example, when posed in a position 
looking away from the camera, will often turn 
their heads when hearing the click of the shutter. 
When exposing for portraits and giving a time 
exposure with a roller blind shutter, it is a good 
plan to pull the cord gently so as to raise the 
blind and to release it before it reaches the half- 
way click, at which it remains open; the spring 
will pull the blind down again if the click is not 
passed, and in this way an absolutely silent 
exposure may be made. For exposures for self- 
portraiture, printing, enlarging, etc., see under 
those headings, and also *‘ Exposure Tables.”’ 


EXPOSURE 

It is scarcely necessary to emphasise the great 
importance of correct exposure in negative 
making; but it may be remarked that when the 
plate has been correctly exposed, all subsequent 
work is comparatively simple and straight- 
forward, whereas with an incorrectly exposed 
plate all the subsequent operations are difficult 
and unsatisfactory, and the production of a good 
print is sometimes impossible. 

The correct exposure of a plate depends on 
four varying factors: the subject; the light, 
which varies according to the season, the time of 
day, and the weather; the speed of the plate ; 
and the “‘ rapidity,” or working aperture, of the 
lens. 


—— 


Exposure 


In the earlier photographic days no attempt 
was made to work systematically from these 
four varying factors, but exposures were largely 
the result of guess-work. About 1880 the first 
attempts were made to systematise the data 
from which exposures were calculated, Dr. 
Scott’s table of light values, and W. K. Burton’s 
table of comparative exposures for different sub- 
jects being among the earliest examples of their 
kind. Dr. Scott determined the fact that the 
value of daylight varied in direct proportion to 
the height of the sun above the horizon. Con- 
sequently, in equally clear weather, exposures 
would require to be nearly four times as long in 
the middle of December as in June; and also at 
six o’clock in June exposures would be three 
times as long as at mid-day. Dr. Scott pub- 
lished a table, about 1883, giving proportionate 
figures for each hour of the day for the middle of 
each month. Although these figures were 
necessarily incomplete, the interval from one 
month to the next being much too long, this 
table proved to be of valuable assistance for 
many years, 

Burton’s tables provided a series of com- 
parative exposures for different subjects—land- 
scapes, marine pictures, interiors, and portraits— 
under normal conditions. It gave the exposures 
under the best possible conditions, and these had 
to be multiplied by the figures given in Dr. 
Scott’s table for all times excepting mid-day in 
June. (See also “ Exposure Tables.’’) 

The most modern method of determining the 
duration of an exposure is by means of a meter. 
(See “ Exposure Meter.’’) 

In process work, and colour work, the lengthen- 
ing of exposure due to prisms, mirrors, colour 
filters, or ruled screens becomes an important 
consideration. The larger the prism the more 
light is absorbed. With a 3-in. prism the expo- 
sute in the case of wet collodion work and 
enclosed electric arc light is increased by about 
2} times; but this would not be true, for 
example, with an orthochromatic plate and green 
filter. Mirrors when in best condition do not 
greatly affect the exposure, but they will do so 
as they become tarnished and scratched. The 
ratio of exposures for colour filters should be 
determined by photographing black, white, and 
a scale of neutral greys, which should come alike 
on all three negatives. Ruled screens increase 
the exposure by about one-fifth, and as small 
stops are used the exposure will be much longer 
than in ordinary negative making, though pro- 
portionately the same. The nature of the 
“copy” (the original) influences the exposure 
in half-tone work. A deep red toned print will 
require the longest exposure. 


EXPOSURE, EFFECT OF TEMPERATURE 
ON (See ‘‘ Desiccated Dry Plates.’’) 


EXPOSURE, INCORRECT 

Correct exposure is the basis of all successful 
work in photography. But in some subjects, 
especially those with moving objects or very 
dark interiors, it may be impossible to expose 
sufficiently long; and occasionally errors of 
judgment may lead to both under- and over- 
exposed plates. 

Incorrectly exposed plates fan always be more 


229 Exposure Meter 


successfully treated if the error is known before 
development is begun than if it is only recognised 
when the operation has made considerable pro- 
gress. Under-exposure is the more difficult to 
treat, as there is insufficient light-action. If 
the subject is one that is deficient in contrast, 
or exposed in a dull light, the best method is 
prolonged development either in a normal solu- 
tion, or in one containing the normal amount of 
developing reagent and excess of alkali. If 
the subject is strong in its contrasts of light and 
shade, prolonged treatment in a normal solution 
considerably diluted, or in a diluted solution 
with extra alkali added, is the only satisfactory 
method. The diluted solution lessens contrasts 
considerably ; and it allows prolonged develop- 
ment without obtaining much strength in the 
light tones. Detail is obtained without density, 
and greater softness results than can be obtained 
by any other method. If the resultant negative 
is still too harsh, the methods given under the 
headings “‘ Hard Negatives,” “‘ Harmonising Con- 
trasts,’’ etc., must be adopted. 

Over-exposure within moderate limits comes 
within the latitude of the plate (see ‘‘ Latitude 
in Plates’’), and requires no special treatment, 
provided that the subject is one of good con- 
trast of light and shade. If a plate has received 
an exposure from one and a-half times to twice 
the normal amount, development may be normal ; 
and though the plate will look very strong, and 
different from one that has been correctly 
exposed, the resultant print will be little, if any, 
inferior to that yielded by a normally exposed 
plate. The time of printing will be much longer, 
and that will be the only difference. In moder- 
ate over-exposure in subjects deficient in con- 
trast, for copying, etc., the only efficient means 
of correcting over-exposure in development is 
by treating it throughout by a modified solution. 
Potassium bromide may be added to a normal 
developer in any quantity up to 2 grs. to each 
1 oz. of solution; or a more concentrated 
developer may be employed, and 3 grs. or 4 grs. 


of bromide added to each I oz. 


Another method of working is to develop 
either with a normal or a concentrated solution 
until the extreme shadows begin to veil; then 
stop development and fix the plate, afterwards 
intensifying to bring it to full printing strength. 


EXPOSURE INDICATOR (Fr., Marquer auto- 
matique, Compteur, Enregistreur; Ger., 
Zihlvozzichtung, Plattenzdhler) 

A mechanical contrivance fitted to magazine 
cameras to indicate the number of plates that 
have been exposed. Usually, the number of the 
plate in position for the next exposure is made 
to show at a small opening, directly the pre-, 
viously exposed plate is moved out of the way by 
the changing arrangement. One pattern has the 
numbers of the plates engraved on a metal wheel 
inside the camera, which is moved round one step 
by the action of the changing lever or handle, each 
time this is worked. There are other patterns. 


EXPOSURE METER (Fr., Photométre, Luci- 
métve, Actinométre; Ger, Exposttions- 
messer, Belichtungsmesser, .iktinometer) 

An instrument for ascertaining the necessary 
duration of exposure when taking a photograph. 


Exposure Meter 


The terms “exposure meter’? and “ actino- 
meter’’ are often used interchangeably, but the 
latter refers to an appliance for simply testing 
the actinic power of light, whereas the former 
means an instrument that not only does this, 
but indicates also the exposure requisite under 
such conditions, with any given subject. While 
an exposure meter may be an actinometer, an 
actinometer is not an exposure meter. The term 
actinometer now tends to be restricted to 
appliances used for finding the light value when 
printing, as in the carbon and similar processes, 
where no visible image is at first obtained. 

Of the many different kinds of exposure meters 
proposed the best are those that provide for an 
actual test of the light intensity ; among these 
may be mentioned the Watkins and the Wynne 


A. Watkins’ Standard Exposure Meter 


devices. The Watkins Standard Exposure 
Meter A has an enclosed chain pendulum for 
counting seconds or half-seconds, the cap or lid 
shown on the left forming, when removed, the 
weight of the pendulum. At the opposite end is 
an opening under which runs a coil of sensitive 
paper, which may be pulled out through a slot 
as required, in order to expose a fresh portion 
under the aperture. To use the meter, a new 
piece of paper is brought into position and 
quickly covered with the thumb, pointing the 
meter towards the source of the light that falls 
on the object to be photographed. The pen- 
dulum is then started swinging, and the finger 


ARASMS DR 
nae SPEED Ay 


B. Watkins’ Watch-form C, Wynne’s Watch-form 
Exposure Meter Exposure Meter 


at the same time removed from the test paper. 
The number of seconds taken by the paper to 
darken to the depth of the standard tint, as 
painted in the circle beside the opening, is now 
carefully counted. The pointer P is then set 
against the plate speed number, the pointer p 
to the diaphragm number, and the pointer A 
to the actinometer time just obtained, when the 
correct exposure will be indicated by the pointer 
E. When the light is weak, or with specially 
dark subjects, the exposure of the camera and 
the meter may be carried out simultaneously, a 
second tint being provided, which the sensitive 
paper takes only one-quarter the time to match. 
This instrument is very complete, and permits 


230 


Exposure Tables 


of special calculations for other than ordinary 
subjects, such as enlarging, copying, etc. 

A simpler form of the Watkins meter B re- 
sembles a watch. Fresh paper is adjusted under 
the opening by rotating the back of the case, and 
the diaphragm number on the inner ring is set 
against the plate speed; the required exposure 
will then be. found against the actinometer 
time. 

Wynne’s “Infallible Exposure Meter” C 
also resembles a watch. A small disc of yellow 
glass (not shown in the illustration) is cemented 
to the revolving dial to cover the sensitive paper 
until it is wanted. It is thus possible to see to 
adjust fresh paper under the aperture without 
its being prematurely exposed to light, and to 
have it always ready by merely sliding aside the 
yellow disc. The Wynne meter has the valuable 
feature of showing at once the necessary expo- 
sure with all the different stops. A table is 
supplied with the meter assigning to the various 
makes of plates a speed number, which repre- 
sents also a diaphragm number. To use the 
meter, the actinometer time on the inner ring, as 
found with the sensitive paper, is set against the 
plate speed on the outer circle. Against each 
of the diaphragm numbers on the latter will 
then be indicated the correct exposure. 
Obviously, if a stop corresponding with the plate 
speed number is used, the exposure will be 
identical with the actinometer time, and the 
camera and meter may be exposed simulta- 
neously. 


EXPOSURE NOTEBOOK (Fr., Registre des 
expositions ; Ger., Expositionsbuch) 

A notebook specially ruled for entering full 
particulars of each exposure made, for the 
after identification of the different negatives, or 
in order that any particular plate may receive 
individual treatment. Spaces are usually pro- 
vided for details of subject, date, time, light, 
plate, number of slide, lens, stop, exposure, etc. 


EXPOSURE, OVER- 
Incorrect.’’) 


EXPOSURE TABLES 


Tabulated series of comparative exposures for 
different subjects, variations in the actinic value 
of the light due to the season, and the different 
lens apertures and plates. They materially 
assist experienced workers when attempting 
unusual subjects; to the inexperienced they are 
extremely valuable, rendering the problem of 
exposure comparatively easy. 

Of the many tables that have been produced, 
attention will here be directed to the series 
designed by Henry W. Bennett, these comprising. 
a table of comparative exposures for different 
subjects, and a diagram and table of the variation 
in the value of the light due to the season of 
the year and the time of day. 


Exposures for lens aperture f/16, plate 200: 
Hurter and Driffield, and the best possible con- 
ditions of light, etc., at mid-day in June :— 

TABLE I 

Open-air Subjects 


(See “‘ Exposure, 


Second 
Clouds ° e ° . e e e 
Boats at sea, distant . ° ° ° . te 


Exposure Tables 
te Second 
Boats at sea, near. ° ° ° ° - oy 
Sea beach, waves, etc. . . . . - ve 
Landscapes :— 


Open common; or open subject with no 


strong objects ° : ‘ - 
Average landscape: cottages or trees in pro- 
minent position : , ‘ 3 eee | 
Trees in full leaf near camera . é AE 
Trees in full leaf very near; part of trees only 
included in picture . 4 ; ; Pe 
Woods: photographs taken under strong 
foliage . . . ‘ ‘ . I.to 5 
Buildings :— 
Large buildings, general views . ° - 
Cottages, small buildings ° ‘ Tee 
Street scenes A A ‘ . ‘ : $ 
Narrow streets . ‘ Pi . Ne 
Details of buildings . . ° ; $ to 4 
Portraits :— 4 
Group or full-length figure . ® * See’ 
Head and bust . : ' 5 ‘ re 
Still-life, flowers, etc., full-size Pay 
Larger objects, according to distance . to} 


Interior Subjects 
Cathedrals and churches :— 


Nave or general view 45 sec. to 2 min. 


Aisles, white glass windows. ‘ I to 3, min. 
Aisles, stained-glass windows s 2 to 7 min. 
Choir i" ‘“ a DAO. SS opin. 


Crypt > a . s 
Ordinary rooms in modern houses . 1 to 3 min. 
Workshops . é P : 30 sec. to I min, 
Rooms or workshops with skylights 10 to 20 sec. 
Portraits in well-lighted room Io to 25 sec. 
Still-life, flowers, etc., full-size, near 

window . ‘ . Io sec, to r min. 

All the above times are sufficient to secure a 
fully-exposed plate. The boats at sea described as 
“near”’ are those that nearly fill the plate; those 
called “‘distant’”’ are small in relation to the size 
of the picture. In the landscape subjects de- 
scribed as “‘open common,” etc., are included all 
those that have no object with any depth of 
shadow within one hundred feet. Small bushes, 
lower than the camera, can be disregarded, as 
the camera, in looking downward, photographs 
them from above, the direction in which the 
light reaches them. In all landscape work, 
heavy foliage will require a longer exposure than 


ro to 60 min, 


TABLE II 


Barer araiis 
PAN iveasiR 
VATA AAA Ary || 
LT YE I | 


U 
a 
BaP 
4 
a 


NI 


J] 
(Es 
on 
SI 
SJ 
~~ 
= 
i 
] 
= 

o 
ins 
= 
= 
sa 
Ba. 
I 
om 


TAL ALY AA | 
ALITY VIAA 
COVEY 


CAT 


a 
a 
PERRET ESS 
JUNE JULY AUGUST SEPTEMGER OCTOBER NOVEMBER DEG 
2 8 6 2 6 tH SH 6H lH ek UB 8 8 ll 
JUNE may APRIL MARCH FEBRUARY JANUARY 086 
= 2 @ Ty 2.7 tt wR Cre eS eS ee a ee 


any other subjects at the same distance, on 
account of its colour and strong deep shadows. 

In all the interior subjects, a range of expo- 
sure is given. ‘The shorter is for a well-lighted 
subject with large and unobstructed windows, 


Exposure Tables 


the longer for one that is comparatively dark, 
with small windows or those seriously obstructed 
by outside objects. Dark woodwork in churches, 
especially if near the camera, will always necessi- 
tate a longer exposure than if the subject con- 
sists of light-coloured stone. In domestic 
interiors, the same principle regarding windows 
applies equally ; and the colour of the walls and 
the furniture will also affect the exposure. In 
the case of an unfurnished room, the exposure 
may be reduced to half that given in the tables. 
The exposure for flowers and still-life subjects 
will be influenced by the colour, the degree of 
contrast, and also by the manner in which the 
light from the window falls on it. 

These exposures, being correct for the best 
possible light in June, must be multiplied by 
the figures obtained from the graph (called 
** Table IT.’’), in which the thicker horizontal lines 
represent the hours and the fine horizontal lines 
quarter-hours. The fine vertical lines corre- 
spond to intervals of five days for each division, 
the dates being given under every alternate 
line. It is practicable to read off the correct 
figure for any day, and for any time in the day. 
Hach thick curved line has its multiplying figure 
shown on it. This figure is indicated for any 
date and time by the point at which these curved 
lines cross the horizontal and vertical :— 


TABLE III 
VALUE OF DAYLIGHT THROUGHOUT THE 
YEAR 

on me) (2) 2) ° 

H N N ie) N 

ala) slelelsiels|§lsfe 

S215 |S 8/6 [Sle |8 

SIO (kde 1D 13 lo [Flo [9 

ml almnlalm!S)elg lala lion 

alalarclx feist elelele 

SISISIZIS IS (S/S iS S18 
a.m. p.m. SSIS SSS |e IG IS|S| a.m. p.m 

12.0 : I] 1] r |xrdix4/14) 2 [23/23] 3 | 4 12.0 

II.O 1.0/1] 1 |rd/14/r4) 2 124) 3 [34] 4 [44] 11.0 1.0 
10.0 2.0 | 1 |r¢/14/14|2/2131414]5|6| 10.0 2.0 
9.0 3.0 |rf/r14/14) 2 |24/3 1415] 8|r0\12| 9.0 3.0 
8.0 4.0 {14/14} 2 |23) 3 [44] 6 |12 8.0 4.0 
7.0 5.012/2!13/41/5|8 |20 
6.0 6.0]3/3|4]|6|12 
5.0 7.0]5]6|10/20 


In Table III. it is only practicable to give 
multiplying figures for'each hour and for every 
fifteenth day. The variations for intervening 
times and dates can be estimated. This day- 
light table disregards the effect of the weather. 
When the light shows any appreciable departure 
from the best for the time of year, the exposure 
should be multiplied by 2; if the weather is 
dull, multiply by 3; and if very dull or gloomy, 
by 4 or 5. 

These exposures are for a plate having a speed 
of 200 H. and D. Most modern rapid plates are 
about this speed, but the makers give the rapid- 
ities in almost all cases. The exposure for other 


plates will be directly proportionate to their 


Exposure Tables 


rapidity; thus a plate 100 H. and D. will 
require twice the exposure of one having a speed 
of 200 H. and D. 

These exposures are for f/16, a medium aper- 
ture. The relative exposures for other apertures 
ate given in Table IV. 


TABLE IV 
Value of Diaphragm Apertures 


Fis‘6 f/8 flax fi16 fl22 fi32 flas  f/64 
$ t 4 I 2 4 8 14 


The exposure for any subject is first found 
from Table I.; this is multiplied by the time 
value from Table II. or III.: the result is multi- 
plied by 2, 3, etc., if dull weather, and finally the 
total is multiplied by the stop value from Table 
IV. Otherwise expressed :— 


Subject x Time value x Weather x Lens aperture 
Table I. Table II. or III. Table IV. 


The result being the exposure required 

Two examples will render the method of 
working more easily understood. (1) For open 
country lane with cottages in the mid-distance, 
September 14, 2 p.m., a fine, clear day, stop 
J/32, plate 200 H. and D. :— 


Time : 
Subject Sep. 14 Weather Stop f/32 Exposure 
2 p.m; 
$°SeG. XK ae TX r x 4 = I sec, 
(2) A cathedral aisle, well lighted by stained- 


glass windows, April 17, 10.30 a.m., slightly dull 
[2], lens aperture f/22, plate 200 H. and D, :— 


Time : 

Subject Ap. 17 Weather Stop f/z2 Exposure 
10.30 a.m. 

2 min. xX 14 4 2 x 2 = #£412min. 


Instead of using Table II. or III. and multi- 
plying again for the weather, a meter may be 
substituted as a means of measuring the intensity 
of the light. The multiple of the unit time that 
is required for darkening the sensitive paper to 
match the standard tint is the figure to be used 
in multiplying the unit exposure obtained from 
Table I. The meter should always be held in a 
vertical position, facing the camera. As an 
example, the same data may be taken as in 
No. 1 illustrating working from Tables I. and IT. 
A country lane with cottages, September 14, 
2 p.m., stop f/32, plate 200 H. and D. Assume 
that a Wynne meter is used to test the light, the 
unit time for matching the painted tint being 
four seconds. It is held vertically, facing the 
camera, and the time required for matching the 
tint is eight seconds, twice the unit time. 


Subject Meter Stop Exposure 
(Table I.) (units) F/32 
$ sec, x 2 x 4 = 1 sec. 


A meter can be used in a very simple manner 
for determining the exposure of objects within 
twenty feet of the camera, by giving a definite 
proportion of the time that the paper takes to 
darken to the standard tint. ‘The Wynne 
standard tint requires four seconds, the Watkins 
standard eight seconds, and the lighter of the 
two tints supplied with the Watkins Bee meter 
four seconds for matching with the sensitive 


232 


Extension, Camera 


paper in the best possible light. Consequently, 
in the following table, different proportionate 
figures must be employed according to the 
meter used. 

To use this table, which is very useful for still- 
life, flowers, portraits, animals, machinery, etc., 
the meter is held close to the subject in a 
vertical position, facing the camera. The 
actual time that the paper takes to match the 
standard tint is noted, and a definite proportion 
of this time is the correct exposure without 
regarding it as a multiple of the standard time. 
This proportion varies according to the distance 
of the subject from the camera. 


TABLE V 


The exposure will be the following proportion 
of the actual time that the meter paper requires 
to match the standard tint :— 


Distance of Wynne and Watkins 
subject from Watkins Bee standard 
camera light tint tint 
3 feet one-half one-fourth 
3 ise one-fourth one-eighth 
To. 4; one-eighth one-sixteenth 
20: + one-sixteenth one-thirty-second 


These exposures are for f/16, and a plate 200 
H. and D. j 

These exposures are for objects of medium 
colour; for very dark subjects the exposure 
should be doubled; for very light, it may be 
reduced to one-half, 

Two examples will illustrate the method. A 
portrait, head and bust only, is being taken in a 
garden. The sitter is about five feet from the 
camera, and a Wynne meter, held close to the 
sitter and facing the camera, requires four 
seconds to match its standard tint. ‘The expo- 
sure for f/16 and a plate 200 H. and D. will be 
one-fourth of this time = 1 second. 

A small machine is being photographed in a 
workshop, the same plate and stop f/32 being 
employed, and the machine being about ten feet 
from the camera. The day is dull, the work- 
shop not well lighted, and the meter, placed on 
the machine while the camera is being arranged 
and the image focused, requires fourteen minutes 
to match the standard tint. One-eighth of this 
time for ten feet distance, one minute and 
three-quarters, multiplied by 4 for {/32, gives 
7 minutes as the exposure required. 


EXPOSURE, UNDER- (See “Exposure, 
Incorrect.’’) 


EXPRESSTYPIE 

A’ process of making grained half-tone blocks, 
invented by Cronenberg. It consists in the 
use of a grained screen, placed in contact with 
a gelatine dry plate so as to make a grained 
negative. ‘This is printed on to zinc or copper 
in the usual way. The grain is of a reticulated 
character resembling collotype. 


EXTENSION, CAMERA (Fr., Extension: Ger., 
A usdehnung) 

The distance between lens and plate, or the 
length to which the bellows will rack out. (See 
“Double Extension” and “‘ Camera.’’) 

Also the name given to an accessory for length- 
ening this distance, when the bellows do not rack 


Exteriors, Photographing 


out far enough for the special work in hand. 
There are many different kinds of camera 
extensions, or “ adapters,’ for this purpose, 
some fitting on the front of the camera, others 
at the back. 


EXTERIORS, PHOTOGRAPHING 

The general technical considerations that have 
to be observed in photographing exterior views 
of buildings, etc., are given under the heading 
** Architectural Photography.’’ There are, how- 
ever, several special considerations which cannot 
apply in the same manner in interior work. 
Speaking generally, a long-focus, rather than a 
short-focus, lens should be employed. At times 
there are advantages in using a short-focus lens 
for a comprehensive view of a high building, but 
in small details or portions the longer focus is 
always preferable when practicable. Of course, 
there are many cases where limited space or 
other conditions render it impossible to use any 
other than a wide-angle lens. There is one 
respect in which a wide-angle lens assists the 
photographer to secure an effect that cannot 
be obtained by any other means. In photo- 
graphing a high building from the near point of 
view necessitated by a wide-angle lens, the 
impression is conveyed of looking upwards in a 
manner that cannot be given by any photograph 
taken from a more distant point. The effect 
is realistic. 

Whether photographing a complete building 
or a small portion or detail, an oblique view 
should practically always be taken. A square 
front view is like an architect’s drawing; it is 
never satisfactory, as it fails to give a fair 
impression. An oblique view gives at once a 
good impression of the relief and the form of 
the building or detail. It conveys the impression 
of solidity, and not simply the outline of the 
front elevation. Sunshine is very effective, and 
very useful in giving relief as well as good effect. 
More especially is this the case with large sub- 
jects; small details are frequently more satis- 
factory in diffused light. Very fine effects can 
sometimes be obtained by taking a photograph 
when the sun is shining almost along the surface 
of the subject, very slightly in front. The long 
cast shadows from projecting details are strik- 
ingly effective. A liberal proportion of fore- 
ground should be included in any pictorial view 
of a building, or doorway, or similar detail. 
And where possible, a foreground with lines 
running obliquely into the picture should be 
chosen. Itis the most simple and telling manner 
of conveying the impression of the space that 
exists between the object and the observer. As 
in interior work, the point of view, the lighting, 
and the general conditions should be chosen so 
as to show in the most effective manner the 
character, the quality, and the special features 
of the architecture photographed. 


EXTRA-FOCAL DISTANCE, OR ‘‘E.F.D.”’ 

The distance between lens and object, and lens 
and image, minus the focal length of the lens. 
The greater E.F.D. equals focal length multipli 
by ratio. The lesser E.F.D. equals focal len 
divided by ratio. 


233 


Eyepiece, Focusing 


EYE LENS 

The lens, or combination of lenses, of an eye- 
piece which receives the image from the field 
lens and conveys it to the eye, as explained 
under the heading ‘‘ Eyepiece.” 


EYEPIECE (Fr., Oculaive ; Ger., Okular) 


The lens, or combination of lenses, which 
receives the image from the microscope objec- 
tive and conveys it to the eye. The best known 
types of eyepieces are the Huyghenian, the 
Ramsden, and the Kellner. 

The Huyghenian, which is the most popular, 
is a negative combination composed of two 
plano-convex lenses separated by the distance 
of half the sum of their foci. The lower lens of 
an eyepiece, that nearest the objective, is 
known as the field lens, and the other is the 
eye lens. A stop is placed between the field 
and eye lens at the principal focus of the 
latter. 

The Ramsden, which is a positive and achro- 
matic eyepiece, is a combination of two plano- 


. convex lenses with their convex surfaces inwards. 


This form is especially useful for micrometric 
purposes. The Kellner eyepiece is now rarely 
used ; it gives a very large field, but the defini- 
tion is not equal to that of the Huyghenian, The 
eye lens is a combination of a biconvex (field 
lens) and a biconcave lens (eye lens). 

The projection eyepiece, as its name implies, 
is designed exclusively for lantern and photo- 
graphic work. The field lens of a projection 
eyepiece consists of a plano-convex lens, the 
eye lens being a biconvex combination of three 
lenses. ‘The field of this eyepiece is very limited, 
but it gives fine definition; the magnification is 
small, from 2 to 6 diameters. The compensating 
eyepiece is designed to be worked in conjunction 
with apochromatic objectives. This eyepiece 
derives its name from being over-corrected to 
compensate for the under-correction of the 
apochromats. The compensating eyepiece works 
well with high-power, but indifferently with low- 
power, achromatic lenses. The eye lens of the 
compensating ocular is plano-convex and the 
field-lens a biconvex triplet, the eye lens and 
field-lens being placed in close juxtaposition. 

There are no universal standards for either 
diameter or magnification of eyepieces. The 
Royal Microscopic Society has adopted four 
standard sizes for eyepieces—namely, No. I. 
0°9173 in. (23:3mm.); No. II. 1-04 in. (26-416 
mm.); No. III. 1-27 in. (32°358 mm.); No. IV. 
1°41 in. (35:814 mm.). The variety of methods 
of classifying the initial magnification or power 
of an eyepiece is even more unsatisfactory than 
the lack of uniformity in size. In most English 
eyepieces the initial magnification is indicated 
by letters A—E, A representing the lowest power 
listed by the particular firm, giving a magnifica- 
tion of 4 or 6 diameters; the initial magnification 
of E would be from 12 to 20. On the Continent 
figures, not letters, are used to classify the power 
of the ocular, but they give little clue to the 
magnification. 


EYEPIECE, FOCUSING 
Magnifier.’’) 


(See ‘‘ Focusing 


F 


‘*F*? NUMBERS 

A popular method of marking diaphragms or 
stops, the smaller f or the capital letter being 
used with the number, as, for example, f 8, f11, 
etc. (For full particulars of measuring, relative 
values, etc., see under the heading ‘“ Dia- 
phragms.’’) 


FABRICS, DARK-ROOM 

Canary, orange, or red translucent cloth, used 
instead of coloured glass for screening the light 
in dark-room illumination. They are more 
serviceable when used with artificial light, as 
sunlight causes them quickly to fade and 
become unsafe. The canary fabric is generally 
used for slow bromide papers; the orange for 
rapid bromide papers, lantern plates, and slow 
dry plates; and the red for rapid dry plates. 
Fabrics are, as a rule, quite as safe as glass, but 
pinholes must be watched for, and the fabrics not 
wetted in any way or exposed to strong sunlight. 


FABRICS, PRINTING ON 

Fabrics already sensitised for the bromide 
and platinotype processes may be purchased, 
and they are used in the same way as bromide 
and platinotype papers. Fabrics are easily pre- 
pared for photographic printing, and the blue- 
print process is perhaps the simplest. The 
fabrics mostly employed are cottons, linens, 
silks, nainsooks, etc., but silk that has been 
weighted with mineral matter is unsuitable; 
the finer the material the better. The fabric 
needs to be thoroughly washed in hot water, 
ironed, and, to prevent the image from sinking 
into the material, it should then be well sized, a 
suitable size being— 


Arrowroot : » 80-98 8 g. 
Gelatine . ; - eS eas "3 as 
Alum : . RPA eh A ae 

‘ Water to. “ 20 OZ. 1,000 ccs. 


The fabric is immersed in this solution for about 
five minutes, pinned down on to a flat board, 
and dried before a fire, it being then somewhat 
stiff. The ammonio-citrate and ferricyanide 
sensitising solution (see ‘‘ Blue-print Process ’’) 
is then brushed over it, and, after drying, it is 
teady for printing upon. Printing, washing 
(fixing), etc., are exactly as described for blue 
prints upon paper. The printed fabric will not 
withstand washing with soap and water, as the 
alkali destroys the blue image. 

In order to get the best and brightest of blue 
prints upon fabrics, it is necessary to use a 
negative with strong contrasts—that is, one 
with clear shadows and dense high lights, and the 
negative should show broad effects of light and 
shade rather than an abundance of fine detail. 

A process for the replacing of the blue ferro- 


234 


ptussiate image by various dyes was published 
in 1898 by Stewart E. Carter. Bleached cotton 
or linen is brushed over with a ferro-prussiate 
sensitiser, made as follows :— 


A. Ferric ammon. citrate 164 grs. 164 g. 
Distilled water to I OZ, « 400 cca, 

B. Potass. ferricyanide . 164 grs. 164 g. 
Water to : . I OZ. 500 ccs. 


A and B are mixed in equal parts. The sensi- 
tised fabric is exposed and washed just as a print 
upon paper. The blue print is next immersed 
in a weak solution of caustic soda (5 grs. to I oz. 
of water) for a few minutes, then washed in 
hot water, and placed for three minutes in a 
solution of 13 grs. of sodium phosphate in 10 oz. 
of water at a temperature of 170° F. (about 
77° C.). This is followed by washing, first in 
cold water and then in hot water, after which 
the print is ready to receive the dye. A weak 
gelatine solution is made (glue size 24 grs., 
water 10 oz.) and heated to 160° F. (71° C.), 
and the prints moved about in it for about 
three minutes; from 3 to 5 grams per litre 
(1°3 to 2:2 grs. per ounce) of dinitroresorcin 
(resorcin green) is added, and the temperature 
raised to 180° F. (82° C.). As soon as the shade 
is considered full enough for a strong picture, 
remove to boiling water to wash out all unfixed 
dye. The high lights (whites) are next cleared 
in a bath of neutral soap (used at a temperature 
of 160°F., 71°C), and the print again washed 
in hot water and finally in cold. Other dyes 
may be used in place of the green named. 
Gallo-cyanine gives blue and violet; alizarin 
gives purple, and also a brown sepia. The original 
blue print may be toned, but the dye method, 
although rather troublesome, gives the more 
pleasing effects. 

Carbon prints may be transferred to any kind 
of fabric. This must be washed, dried, ironed, 
and given several coats of the following sizing 
mixture, allowing to dry after each coat :-— 


Cooking gelatin s > OE 133 g 
Sugar . ls Pape ere 66's 5; 
Glycerine . : 4 aie 66 .ccs 
Chrome alum I5 grs 2 
Barium sulphate 2 az 266 ,, 
Water to. : | a 1,000 ccs. 


Dissolve by heat and mix thoroughly. Transfer 
the carbon tissue thereon in the usual way. (See 
** Carbon Process.’’) 

Fabrics can be sensitised and used as ordinary 
P.O.P. First soak the washed and dried fabric 
in the following size for about three minutes :-— 


Gelatine . 100 gts. IO g 
Common salt 2, FOO Sy BO 3; 
Magnesium lactate . 100 ,, ur; 


Water to. ° » 2O/Og, 1,000 CCS. 


Factorial Development 23 


Dissolve by aid of heat and then well mix; 
after coating the fabric allow it to dry thoroughly. 
The sized fabric is then sensitised by soaking 
for three minutes in— 
Silver nitrate 25 grs. ge. ¢ 
Distilled water to I OZ, + £000 ccm 


The fabric is next immersed for one minute in— 


Citric acid : . §0-grs. 5 g. 
Sugar i : cD inc) “3 
Water to. ‘ eee 4, 1,000 ccs, 


and dried in the dark. The sensitive fabric is 
then printed upon, toned, fixed, and washed 
exactly as ordinary P.O.P. 

An easier method of coating fabric with a 
silver solution is the following: A salting or 
sizing bath is first made by rubbing up 180 ers. 
of arrowroot or dextrine in a little cold water 
until a smooth paste results; make this up 
to # pint with boiling water. If the mixture 
does not at once become gelatinous it should be 
kept hot (not boiling) and stirred till it does. 
It should then be allowed to cool a little, and 
160 grs. of ammonium chloride dissolved in 
about 4 oz. of water added to it. The mixture 
is applied while warm to the washed and ironed 
fabric, which is then dried and sensitised in 
the following bath :— 


A. Citric acid 25 grs 50 g. 
Distilled water. 4 02. 500 ccs. 

B. Silver nitrate 60 grs 125. 2. 
Distilled water. 4 oz. 500 ccs. 


Mix the two solutions. To sensitise the fabric 
use a Buckle or Blanchard brush. Pin the 
fabric to a flat board, pour upon it a little of the 
silver sensitising mixture rapidly and evenly, 
spread it over the entire surface, and dry in 
the dark. The fabric is printed upon as though 
it were P.O.P., toned with an acetate and gold 
toning bath, and fixed and washed like paper. 
It is desirable after washing and before toning 
to pass the print through a weak solution of 
sodium chloride (common salt), which gives 
reddish brown tones, or of sodium carbonate, 
which gives brownish purple tones. (See also 
* Diazotype,” “Indigo Printing,” etc.) 


FACTORIAL DEVELOPMENT (See 
“Development, Factorial.’’) 


FACTORIES, PHOTOGRAPHING IN 
Taking photographs in factories or workshops 
presents difficulties from several independent 
eauses. ‘The first is that work in progress can- 
not always be stopped while the exposures are 
made, and the consequent movement cannot 
always be prevented. Then machinery and 
shafting in constant motion introduce the serious 
element of vibration, and, in addition, smoke 
and moisture are inseparable from some kinds 
of work, increasing the difficulties of securing 
good negatives. When the nature of the work 
will allow it, the negatives should be taken 
during the dinner-hour. The camera can be 
set, everything arranged as desired, the subject 
focused, and everything made ready for the 
exposure beforehand. Then the plate can be 
exposed under the best possible conditions. A 
small stop is almost always necessary for secur 
ing good definition throughout. 


rad 


5 Faded Negatives and Prints 


When figures have to be included and the work 
shown under its normal conditions, the case is 
different. The exposure must necessarily be 
short so as to avoid movement of the principal 
figures, Frequently, a large aperture is neces- 
sary in order to shorten the exposure sufficiently, 
and it may be quite impossible to secure the 
degree of sharpness in the different planes that 
the photographer would desire. In that case, 
the principal objects must be rendered as crisp 
and sharp as possible, and the other parts must 
simply take their chance. Considerable assist- 
ance may be given to the workmen that are 
included by the manner of posing. If they can 
be given a little support, by resting on a tool, or 
putting one of their hands on a machine, how- 
ever slight the support may be, it will materially 
assist in avoiding movement during the exposure. 
A longer exposure can be given without appre- 
ciable movement. A single machine with one 
or two figures should cause no difficulty. In 
subjects of this kind, duplicate exposures should 
always be made. 

Any windows that are in front of the camera 
and included in the picture should be covered 
during nine-tenths of the exposure, and, if 
possible, the covering should be outside. Win- 
dows in front of the camera, but not included in 
the picture, should be covered during the whole 
of the exposure, unless the lens can be shielded 
from them as described under the heading 
““ Interiors, Photographing.” 


FADED NEGATIVES AND PRINTS, RE- 
STORING 
Faded prints are more commonly met with 
than faded negatives, but whichever is treated, 
success is more certain if the actual cause of 
fading is known (see ‘“‘ Fading, Causes of’’). 
When negatives fade the trouble is usually due 
either to insufficient fixing or to insufficient or 
improper washing after bleaching with mercury 
for the purpose of intensification, During the 
year 1900 Sir William Crookes paid particular 
attention to the subject of restoring faded 
negatives—presumably those treated in the 
usual way and not intensified—and the follow- 
ing process is advocated by him. The faded 
dry-plate negative is soaked for three hours in 
distilled water, and then immersed for from ten 
to fifteen minutes (in the dark-room) in the 
following bath :— 


Water . : yh ee 500 ccs, 
Pyro : . + 3 ees. 3 g. 
Sodium metabisulphite 3 ,, Reet 
Sodium carbonate . 36 ,, ae 
Sodium sulphite Go: Oe ae sy, 


The plate is next well washed, immersed in an 
ordinary ‘“‘ hypo” fixing bath for half an hour, 
and then washed in running water for from four 
to six hours. It is then toned with gold, for 
which purpose two solutions are required, one 
of ammonium sulphocyanide (10 grs. to the 
ounce), and one of gold chloride (1 gr. to the 
ounce); for use, 1 oz. of each is taken and 
8 oz. of water added; or, if desired, the com- 
plete bath may be made up as— 


Water : ; IO OZ, 1,000 ccs, 
Am, sulphocyanide IO gts. a. &: 
Gold chloride . de Bats > re 


Faded Negatives and Prints 


The plate is immersed in this bath for about ten 
minutes and finally washed for half an hour and 
dried. The fixing in ‘“ hypo’ can be omitted if 
so wished, although it is desirable. The gold ton- 
ing bath has the property of precipitating gold on 
the image and rendering it of a blacker colour. 

Negatives that have been intensified with 
mercury may fade quickly, and to restore them 
they should be treated with a solution of potas- 
sium sulphantimonate, commonly known as 
Schlippe’s salt. The faded negative is first 
thoroughly soaked and then treated with 20 gers. 
of Schlippe’s salt dissolved in 2 oz. of water, 
until the desired result is obtained; finally 
wash well. 

The fading of prints has always been a trouble- 
some matter. In the old days the necessity for 
thorough fixing and the complete removal of 
the “hypo” was not generally recognised, and 
the question of fading became so important 
that a committee was formed in May, 1855, to 
enquire into the causes, the Prince Consort con- 
tributing £50 to the expenses of the inquiry. 
Since then, of course, many improved papers 
have taken the place of the old ones, and different 
causes have arisen. Platinum prints are said 
never to fade, but nevertheless they sometimes 
appear to change their colour from the original 
pure black to a brownish or yellowish brown 
colour. According to Chapman Jones, such 
prints may be completely brought back to their 
original colour by unmounting and treating with 
a mixture of hydrochloric acid and chlorine 
water, made by adding a few drops of sodium 
hypochlorite solution to dilute hydrochloric acid 
(about one of acid to ten or more of water), 
until the odour of chlorine is distinctly notice- 
able. Neither hydrochloric acid nor chlorine 
water alone is effective, though each does some- 
thing towards the desired end. Several other 
methods have been advocated, but all are more 
troublesome, and not nearly so effective. 

The restoration of silver (printed-out) prints 
is at all times a very risky performance. If they 
are old and yellow, and of value, they should be 
copied—preferably through light blue glass— 
before any attempt is made to tamper with 
them, because of the risk of spoiling the originals. 
‘One process is to bleach the yellowed albumen 
print in a mercuric chloride solution as used 
for intensifying, well wash, and then to develop 
in an old hydroquinone or metol developer 
(without bromide), or preferably to immerse in a 
5 per cent. solution of sodium sulphite, and finally 
wash well. This process is not reliable. An 
elaborate process of restoring silver prints, and 
one for which the inventor (H. Jandaurek) 
was awarded a silver medal in 1888, is as follows. 
Two solutions are required :— 


A. Distilled water 35 OZ. 1,000 ccs, 
Sodium tungstate 608 gts. ae 4 
B. Distilled water I.0Z. 400 ccs, 
Calcium carbonate (pure) 5 gers. 4 g. 
Chloride of lime i wae: eye 
Goldandsodium chloride 5 ,, rae 


The B solution should be kept in a yellow 
bottle or in the dark for twenty-four hours. 
The faded prints are unmounted, well washed, 
and placed in 8 oz. of the A solution to which 
z oz. to 3 oz, of B has been added. They should 


236 


False Images, or “Ghosts ” 


remain in this toning bath until they assume a 
good purple tone, and they are then well washed 
and fixed with “hypo” (1 oz. to 10 oz. of water) 
until all the yellowness has disappeared, which 
may take one hour or more; finally, they are 
washed well. 

As stated above, all print restoration processes 
are more or less unreliable, and need to be used 
with great caution. Any details that have 
vanished from the faded print cannot be brought 
back, and all that the restoration process does 
is to strengthen the weak parts of the print, 
and as much as this can be done equally well by 
making a copy in a proper manner, 


FADING, CAUSES OF 

All silver images, whether negative or positive, 
are formed by metallic silver in an extremely 
fine state of division imbedded in a vehicle 
of albumen, gelatine, or collodion. Everyone 
knows how prone silver, even in the form of 
spoons and forks or ornaments, is to tarnish, 
and consequently it can be well understood how 
much more readily the metal in a finely divided 
state can be attacked. In many cases, particu- 
larly in that of prints, the fading is undoubtedly 
due to imperfect fixation or removal of the last 
traces of “ hypo’’ or the hyposulphite of silver. 
It must not be overlooked that gelatine is a 
hygroscopic substance, and that “ hypo” in the 
presence of moisture is decomposed, giving rise 
to sulphur compounds which readily attack the 
image. Whilst fading is not so commonly met 
with in negatives, it can still be detected some- 
times, and it is then advisable to bleach the nega- 
tive with a chlorising mixture, such as hydro- 
chloric acid and potassium bichromate, wash 
well, and redevelop. 

There is but little hope of saving a fading 
print, and care should be taken to ensure perfect 
fixation and thorough washing, the former being 
as essential as the latter. It will often be found 
that prints mounted on cards show fading more 
readily than those that are unmounted, and 
this may be due to the card containing “‘ hypo ” 
or some sulphur compound which is gradually 
decomposed by the mountant or moisture, and 
acts on the silver image. Frequently, too, 
prints—especially collodion prints—will fade in 
circular spots, and this can often be traced to 
small particles of metal, such as the bronze 
powder used for gilding the edges, etc., electro- 
lytic action having been set up by the acid 
moisture in the air between the two metals, 
Vartnishing negatives and prints is some pro- 
tection. In the case of framed prints care should 
be taken to see that the backboard of the frame 
fits well, that the prints and mount are thoroughly 
dry before being framed, and that all round the 
edges, and over any cracks in the backboard, 
good stout brown paper is pasted or glued. 


FAHRENHEIT THERMOMETER 
“* Thermometer,’’) 


FALLING FRONT (See “ Rising Front.”) - 


FALSE IMAGES, OR ‘‘GHOSTS’’ (Fr., 
Images fausses ; Ger., Falsche Bilder) 


Even the best doublet lenses sometimes show 
what is known as a false image or “ ghost,” 


(See 


False Dispersion 


when a bright object or light occurs in the pic- 
ture. This is due to reflection of the bright 
object from the front surface of the back lens, 
and from this to the back surface of the front 
lens, whenceit is again reflected towards the plate. 
In a properly designed lens, the distance apart 
of the glasses and the position of the stop are 
so arranged that the false image is diffused 
before it reaches the plate, and so is very rarely 
troublesome. To test for the presence of a 
false image, focus a gas flame or a lighted candle, 
placed at a distance from the camera equal to 
about eight or ten times the focal length of the 
lens. Cover the head with the focusing cloth, 
and bring the image of the flame into the centre 
of the ground-glass screen. If the camera is now 
turned slowly so that the image moves to one 
side, the ghost, if present, may on careful 
inspection be seen moving in the contrary direc- 
tion, and exactly opposite the principal image, 
It very probably will not be in focus at the 
same time as the chief image, but it may usually 
be brought into focus by a slight movement of 
the screw, and will then be found to be distin- 
guished from the primary image by being erect 
instead of inverted. This defect may often be 
cured by slightly altering the distance between 
the lenses, or by varying the position of the 
diaphragm, the false image being consequently 
spread over the whole of the plate and not 
allowed to come to a focus. (See also “ Flare 
Spot.’’) 

FALSE DISPERSION (See ‘‘ Dispersion.’’) 
FALSE PERSPECTIVE 

False.’’) 


FARMER’S REDUCER AND INTENSIFIER 

About the year 1883 Howard Farmer intro- 
duced what is undoubtedly the most widely 
used reducer. It consists of “hypo” and po- 
tassium ferricyanide in solution, and is some- 
times referred to as the “ferricyanide” or 
“hypo-ferricyanide,’”’ but more frequently as 
the ““Farmer”’ or “Howard Farmer ’’ reducer. 
It will be found described under the heading of 
** Reducers.” 

Farmer’s intensifier is not so well known. It 
is one of the “silver’’ processes, and will be 
found with others under the heading of “‘ Silver 
Intensifier,”’ 


FEERTYPE 

A printing process, patented by Dr. Adolf 
Feer in 1889, in which paper is sensitised with 
diazo-sulphonic salts of aniline, amido-azo- 
benzol, benzidine, and their homologues, in 
conjunction with compounds of phenol, resorcin, 
or naphthol. The diazo compound is set free 
by the action of light, and forms a colouring 
matter ; thus a coloured positive print is obtained 
from a negative. After exposure, the print is 
washed in water or dilute hydrochloric acid, by 
which means the unacted upon and unchanged 
pteparation is removed. (See also ‘ Diazo- 


type.’’) 
FERGUSON’S TONER 


A copper toning bath for bromide prints. (See 
* Copper Toning.’’) 


(See “‘ Perspective, 


237 


Ferric Ammonio-oxalate 


FERNS AND LEAVES, PRINTING FROM 

Ferns and leaves make effective and decora- 
tive photographs which are easily produced 
without a camera, lens, or negative, the leaves 
being printed direct upon the sensitive paper. 
Lace may also be photographed in the same way. 
Hither fresh, preserved, or skeletonised flowers 
and leaves may be used. A piece of plain glass 
should be placed in a printing frame of the 
desired size and the leaf laid flat thereon, the 
sensitive paper (any kind answers, although 
P.O.P. is preferable) coming next; the back of 
the frame is placed in position, and the whole 
put out to print in the usual way. When 
printed sufficiently, tone or develop, as the case 
may be, and afterwards fix and thoroughly wash. 
When the leaves are particularly moist it is 
advisable to place a thin sheet of celluloid—a 
clean film serves admirably—between the leaf 
and the paper in order to prevent the paper from 
becoming contaminated with the natural juices. 
Almost equally good results may be obtained 
from natural or skeletonised leaves, the differ- 
ence being in the duration of printing. Bracken 
and virginia creeper leaves are particularly suit- 
able, and a brief printing from fresh leaves gives 
the outline of the leaves only, the image appear- 
ing as white upon black. If, however, a reveisal 
is wanted, the leaf may be placed in contact 
with a dry plate and a negative made which 
would produce a print showing black upon white. 
The longer the exposure the more light travels 
through the leaf, and the greater the detail 
obtained. New leaves when suitably printed 
give beautiful half-tones, because of the different 
densities of the various parts of the leaves; 
whereas skeleton leaves produce only black and 
white prints. Talbot, in 1836, used a fern leaf 
when he produced the first silver print on paper. 


FERRIC AMMONIO-CITRATE (F*., Citrate 
de fer ammontacale ; Ger., Braune citro- 
nensadure Eisenoxydammoniak) 

Synonym, ammonium citrate of iron. 4Fe 
C,H,;O0,7 3(NH,)s Cs H307 3Fe (OH)3. Molecular 
weight, 2,030. Solubilities, 1 in 4 water, insoluble 
in alcohol. It takes the form of brownish red 
scales, and is made by dissolving freshly precipi- 
tated ferric hydrate in excess of citric acid and 
neutralising with ammonia. It is sensitive to 
light, and should be kept in the dark. It is 
used in conjunction with potassium ferricyanide 
in the iron printing processes. 

Valenta has recommended a green salt, which 
is a mixture of neutral ammonium ferric citrate, 
acid ammonium ferric citrate, and ferric citrate, 
and has the formula 5FeC,H;O, 2(NH,)3 C,H;O, 
NH, C,H,O, 2H,0. Molecular weight, 1,956. 
This occurs in bright, greenish yellow scales, and 
gives much more sensitive papers with purer 
whites than does the brown salt. It also is 
sensitive to light and must be kept in the dark. 


FERRIC AMMONIO-OXALATE (Fr., Oxa- 
late ammoniaco-ferrique ; Ger., Ammo- 
nium ferrioxalat) 

Synonyms, ammonium oxalate of iron, oxalate 
of iron and ammonia. Fe,(C,0O,4)3 3(NH,)s 
C,0, 8H,O. Molecular weight, 892. Solubilities, 
1 in 2*1 water, insoluble in alcohol. It occurs 
in bright green crystals, and is formed by 


Ferric Ammonio-sulphate 238 


dissolving ferric hydrate in ammonium oxalate 
solution, evaporating and crystallising. It is 
decomposed by light into ferrous ammonium 
oxalate, and is used occasionally for blue prints, 
a formula being :— 


A. Ferric ammonium 


oxalate . - ¥ OZ, 250 g. 
Distilled water to 20 ,, 1,000 ccs. 
B. Potassium  ferri- 
cyanide . . OL 250 g. 


Distilled water to 20 ,, 1,000 ccs, 


Mix in equal parts just before use. It is also 
used in the cold-development platinum and the 
print-out platinum processes. 


FERRIC AMMONIO-SULPHATE (Fr., Sul- 
fate de fer ammoniacale ; Ger., Schwefel- 
sdure Etsenoxydammoniak) 

Synonyms, ammonium sulphate of iron. Fe SO, 
(NH), SO, 6H,O. Molecular weight, 328. Solu- 
bilities, 1 in 5 water, insoluble in alcohol. It 
occurs as pale greenish crystals, and is prepared 
by dissolving 139 parts of ferrous sulphate and 
75 parts of ammonium sulphate in a minimum 
of water and afterwards crystallising. It has 
been suggested as a substitute for ferrous sul- 
phate on account of its greater stability, and it 
has been used for developing wet plates. 


FERRIC CHLORIDE (Fr., Chlorure ferrique ; 
Ger., Eisenchlorid) 


Synonym, perchloride or sesquichloride of 
iron, iron trichloride. Fe Cl,6H,O. Molecular 
weight, 270°5. Solubilities, 1 in -63 water, I 
in 4 alcohol, 1 in 4 ether. It takes the form 
of yellow crystalline lumps, which rapidly 
deliquesce in the air. It is prepared by dis- 
solving iron wire in hydrochloric acid and oxidis- 
ing with nitric acid. It has been recommended 
for reducing negatives, but it gives rise to yellow 
stains due to the formation of basic ferrous 
salts. Its chief use is as a mordant in etching 
half-tone and photogravure plates. 


FERRIC OXALATE (Fr., Ovalate ferrique; 
Ger., Ferrioxalat) 

Synonym, iron sesquioxalate. Fe, (C,O,)s. 
Molecular weight, 376. Solubilities, very soluble 
in water, insoluble in alcohol. It occurs in 
greenish, glistening scales, which are extremely 
sensitive to light, and it is therefore usually 
preferred to mix it in solution and preserve in 
the dark. It is the most light-sensitive of any 
of the iron salts. It is used in the kallitype 
process, but its chief use is as the sensitive salt 
in the platinotype process. The following is the 
best method of preparing the normal ferric 
oxalate solution: Powder some ammonia-iron- 
alum, weigh out 500 grs. or 520 g., place in a 
tall cylindrical graduate, capable of holding 
20 OZ. Or 1,000 ccs., and add 192 minims or 
200 ccs. of liquor ammoniz (-880), and an equal 
quantity of distilled water. Stir well for about 
five minutes, and allow to stand for a further 
five minutes, Then fill up with distilled water, 
stir well, and allow the precipitated ferric hydrate 
to settle down. Next decant or siphon off the 
clear supernatant liquid, and repeat the process 
until the wash water is no longer alkaline to 
litmus paper. Then allow the precipitate to 


Ferric Salts, Printing with 


settle till it occupies not more than 17 oz. or 
850 ccs. Add 2,064 grs. or 215 g. of pure 
oxalic acid in powder, stir well, and allow to 
stand in the dark-room until the precipitate is 
completely dissolved. Now filter the solution, 
and wash the filter paper with distilled water 
so as to make the total bulk of the solution 
20 0Z. OF 1,000 ccs. This forms the ‘‘ normal 
iron solution’’ for platinotype, and contains 
20 per cent. of ferric oxalate with about 1-2 per 
cent. of oxalic acid. 


FERRIC PROTOACETATE (See “ Ferrous 
Acetate.’’) 


FERRIC PROTOSULPHATE (See “ Ferrous 
Sulphate.’’) 


FERRIC SALTS, PRINTING WITH 

The light-sensitiveness of the iron (ferric) 
salts is the basis of a large number of printing 
processes, including chrysotype, cyanotype, 
kallitype, the sepia printing process, amphitype, 
the ink process, and platinotype. In all these 
the ferric salt is reduced by light to the ferrous 
state. The following table (due to Eder) shows 
the comparative light sensitiveness of the various 
iron salts :— 


Ferric chloride and oxalic acid . 100 


Ferric oxalate . ; ; 
Ammonium ferric oxalate. -. .80 
Potassium ferric oxalate pe des ee 
Ferric tartrate . ‘ “is ge Se 
Ammonium ferric tartrate. gs AO 
Ammonium ferric citrate . 4 15 
Ferric chloride and citric acid . 19 


Ferric chloride and tartaric acid 25 


Many of the inorganic ferric salts are com- 
paratively stable to light, but in contact with 
organic matter are readily reduced, as in the 
case of ferric chloride with oxalic or citric acid. 
According to Abney the spectral sensitiveness 
of the iron salts is chiefly in the indigo blue, 
about G4¥F, and extends to — in the green and 
well into the ultra-violet. 

Printing with salts of iron is known as the 
iron-printing or heliographic process. The four 
principal processes, each of which is described 
under its own heading, are: the blue print pro- 
cess (ferro-prussiate), white lines on a blue 
ground; Pellet, blue lines on a white ground ; 
ferro-gallic, black lines on a white ground ; and 
brown line (better known as, and described 
elsewhere in this work under the heading of, 
** Kallitype ’’), white lines on a brown ground. 

An interesting process of printing with a 
ferric salt is Shawcross’s Amphitype (which see), 
in which advantage is taken of the fact that 
these salts have the property of attracting or 
repelling greasy inks. This is again shown in 
the black line ‘“‘ True-to-scale,” or Ordoverax, 
process, where an undeveloped blue-print laid 
on a gelatinous surface will so affect the latter 
as to enable the lines to take ink while the other 
parts repel it. 

The table on p. 239 (due to Eder) gives a very 
clear précis of the principal iron printing pro- 
cesses and the developers necessary to produce 
full vigour of the images, which as a rule are 
only faint. (See also separate headings.) 


Ferric Sesquioxalate 


239 


Ferro-Gallic Process 


Sensitive 


Product of 
salt 


light action 


Developer used to produce full 
vigour of image 


OO SS | | 


Ferric oxalate, Ferrous salt (fer- 


citrate, tartrate, rous oxalate), 
etc. citrate, etc. 
Ditto Ditto 


Ferric citrate Ferrous citrate 


Ferric oxalate Ferrous oxalate 


Ferric oxalate Ferrous oxalate 
Ferric and cupric 


Cuprous chloride 
chloride 


Potassium ferricyanide. (This 
gives insoluble Berlin blue 
with ferrous salts, but a soluble 
compound with ferric salts) 

Potassium ferrocyanide. (This 
gives a blue precipitate with 
ferric salts, but a white with 
ferrous salts) 

Gold chloride. (Where the fer- 
rous salt is formed metallic 
gold is precipitated) 

Potassium chloroplatinite. (Me- 
tallic platinum is precipitated 
where the ferrous salt is formed) 

Silver nitrate 


Potassium sulphocyanide, fol- 
lowed by potassium ferri- 
cyanide. (The cuprous chlor- 
ide is converted into brown 


Colour of Name of 
image process 

Blue Cyanotype. (Gives 
white lines on blue 
ground from a trac- 
ing) 

Blue Pellet’s process. 
(Gives blue lines on 
white ground from 
a tracing) 

Brownish | Chrysotype 
Black Platinotype 
Brownish | Kallitype or Argento- 
black type 


Red brown | Obernetter’s process 


cuprous ferrocyanide) 


FERRIC SESQUIOXALATE (See “ Ferric 
Oxalate.’’) 


FERRIC SODIUM OXALATE (Fr., Oxalate de 
fer et de soude ; Ger., Natriumferrioxalat) 
Synonym, sodio-ferric oxalate. Fe (C,O,)3 
3Na, C,0, 11H,O. Molecular weight, 976. Solu- 
bilities, 1 in 1-69 water, insoluble in alcohol. It 
occurs as large green crystals, unaffected by the 
air. It is prepared by dissolving ferric hydrate 
in acid oxalate of sodium. It is used in the 
printing-out platinum process. 


FERRIC SULPHATE (Fr., Sulfate ferrique; 
Ger., Ferrisulfat, Schwefelsdure Eisenoxyd) 
Synonym, sesquisulphate of iron. Fe, (SO,)3 
9H,O. Molecular weight, 563. Soluble in water. 
It takes the form of greenish crystals, or, in 
the anhydrous form, it occurs as a greyish white 
powder. It has been suggested as a reducer, but 
it gives rise to yellowish basic iron salts in the film, 


FERRICYANIDE OF COPPER (See ‘* Copper 
and Potassium Ferricyanide.’’) 


FERRICYANIDE OF POTASSIUM (See 
** Potassium Ferricyanide.’’) 
FERRICYANIDE REDUCER (Fr., Réducteur 


_ ferricyanure ; Ger., 
Abschwacher) 
The action and use of this reducer are described 
under the heading ‘ Reducers.”’ 


FERRIER AND SOULIER PROCESS 

A method of making lantern slides and stereo- 
scopic transparencies, invented by Ferrier in the 
early days of the albumen process of making 
positives upon glass. The method has been 
kept a trade secret, but is said to be a modi- 
fication of the albumen positive process. 


FERRO-CUPRIC PROCESS 

An iron printing process devised by Obernetter 
about the year 1865. Paper is coated by float- 
ing on the following sensitive mixture :— 


Rothes Blutlangensalz 


engineers, etc., 


Water. . - 100 parts 
Copper chloride (crystals) wo ee 
Ferric chloride solution (sp. g. 


” 


oe om > . 2 ‘ 
Hydrochloric acid : oe he 
The paper is then dried and exposed in the 
same way as “‘ blue-print ”’ paper, a faint image 
being visible. Immediately after printing it is 
floated on the following developing mixture :— 


Potassium sulphocyanide . 10 parts 
Sulphuric acid . ; < I part 
Water. : . < . 1,000 parts 


To this is added 1s parts of the sensitive mix- 
ture given above. If the print is not devel- 
oped immediately after printing the image 
is lost. Development at first should be by 
floating, and when the image has partially 
developed, the paper may be entirely immersed. 
The paper is afterwards well washed and. toned. 
Red tones may be obtained by immersing the 
developed print in a 10 per cent. solution of 
potassium ferricyanide. For purple tones use— 


Ferric chloride . I part 
Ferrous sulphate . . 2 to 24 parts 
Hydrochloric acid . 2 parts 


Water. 10 to 50 parts 


This bath will give a range of tones from red 
through violet and purple to a greenish black. 
Finally wash in weak hydrochloric acid. 


FERRO-GALLIC PROCESS 

A method of printing with ferric (iron) salts, 
giving a black image upon a white ground; 
known also as the black-line process and the 
Colas process. It is largely used by architects, 
for multiplying drawings. The 
following mixture is made up, or larger quan- 
tities in proportion :— 


Ferric chloride yraey 30 grs. 60 g. 
Ferric sulphate . a ae ne” © 
Gelatine . ; eae Bh 
Tartaric acid . Py dab eee 30, 


Water ; ° Pers 1,000 CCS, 


Ferro-Gelatine Developer 


Soak the gelatine in the water, melt by the aid 
of heat, and add the other ingredients. Coat 
paper in the way recommended for the blue- 
print process and dry in the dark. When 
dry, expose under negative or tracing till the 
ground is white and the lines appear yellow, and 
then immerse in the following developer :-— 


Gallic acid 20 grs. 4 g. 
Oxalic acid : oP a, tial 
Water IO Oz. I,000 ccs. 


till the lines are quite black; 
blotting off between clean 
hanging up. 


FERRO-GELATINE DEVELOPER 

A solution of gelatine boiled with sulphuric 
acid so as to lose its setting power, used by 
Carey Lea as an addition to the wet - plate 
developer. 


wash, and dry by 
blotting-paper and 


FERROGRAPHS (See “ Ferrotype Process.’’) 


FERROPRUSSIATE (See “ Blue-print Pro- 
cess.’’) 


FERROTYPE PLATES 

Thin plates of metal coated on their face with 
a fine hard dark enamel. They were so called 
through being prepared as a basis for “ ferto- 
types,” or collodion positives taken direct in 
the camera. (See ‘‘ Ferrotype Process.”’) They 
have, however, another use in modetn photo- 
graphy. A glossy-surfaced gelatine print may 
be squeegeed while wet on to a ferrotype plate 
in exactly the same manner as on to a sheet of 
plate glass. No preparation of the ferrotype 
plate is necessary beyond washing and polishing 
with a soft fabric, and when the prints are dry 
they leave the plate easily with a surface scarcely 
inferior to that produced by contact with glass 


FERROTYPE PROCESS 
type; Ger., Ferrotypie) 

About the middle of the nineteenth century 
the term ‘‘ferrotype” was applied to the process 
introduced by Robert Hunt as “ Energiatype”’ 
(which see), but that process was but little used, 
and the modern ferrotype is quite different. 

Ferrotypes (known also as “ tintypes”’) are 
pictures taken on sheet-iron plates varnished or 
enamelled on both sides, the picture side being 
the more carefully prepared. They are of 
American origin, having been introduced by 
J. W. Griswold in 1855, and were also known 
as “ Melainotypes”’ before the title of ferrotype 
was generally adopted. It is believed that the 
earliest reference made to ferrotypes is in Photo- 
graphic Notes, dated January 1, 1856, announc- 
ing the invention by a Prof, Smith, of Ohio, 
of a process of “ producing a beautiful picture 
on a piece of common sheet iron, . - equal 
to daguetreotypes, and much superior in some 
respects.” The journal calls the pictures 
“* Ferrographs.”’ 

Ferrotype pictures are positives produced by 
the wet collodion process, a black or chocolate 
enamelled iron plate being used as a support 
for the picture instead of glass. The latter needs 
backing up with black paper, velvet, or paint. 
The finished results have the same appearance 


(Fr., Procédé ferro- 


240 


Ferrotype Process 


in both cases, but the ferrotype image is reversed 
as regards right and left, and the process is there- 
fore not suitable for general application. Every- 
one knows that this process has been widely 
used for portraiture by itinerant photographers, 
since by its aid they can take and finish a por- 
trait in the space of a few minutes, The photo- 
gtapher generally takes particular care to arrange 
the sitter “full face,” or in any other position 
in which reversal is not at first detected. For 
ferrotype work ptoper the operator must be 
within easy reach of his dark-room, as the plates. 
are prepared immediately before exposure. 

The process, in brief, is first to prepare the 
plate with collodion, sensitise in a silver bath, 
expose while wet, develop with an iron developer, 
and fix in a solution of potassium cyanide; all 
formule and working details will be found under 
the heading “ Collodion Process (Wet).” . 

The Dry Process.—The introduction of ferro- 
type dry plates has largely displaced the old- 
fashioned wet process; itinerant photographers 
use them in conjunction with automatic cameras, 
which comprise arrangements for developing and 
fixing, thus obviating the use of the old portable 
petambulator-like dark-rooms. Ferrotype dry 
plates are bought in packets and used like other 
dry plates, but instead of yielding a negative 
on glass they give a positive direct upon the 
black iron or tin support. An example of the 
developers used for such plates is: 


Sodium carbonate (pure) 4 ,, 200 g. 
Sodium sulphite a Nee ea 100 ,, 
Hydroquinone . ‘ 4,, re ae 
Potassium bromide . 290 gers. 204 y, 
“Hypo” fixing solution 

(as below) . : 4 02. 25 ccs. 
Warm water to Mey hee 1,000 ,, 


Allow to stand for two days and pour off the 
clear solution for use. In cold weather half the 
above quantity of bromide is required. After 
exposure, the ferrotype dry plate is developed 
until the high lights (which appear brown on a 
white background) and half-tones are well out, 
and the plate is then rinsed in water and fixed 
in a “‘hypo”’ fixing solution (sodium hyposulphite 
4 0Z., water 20 oz.). Development takes from 
eight to twelve seconds in hot weather, twelve 
to twenty seconds in a normal temperature, and 
twenty to sixty seconds in cold weather, After 
fixing (duration, ten to thirty seconds), the plate is 
rinsed for a few seconds and dried spontaneously 
or by gentle heat. It is next varnished, and 
then gives the appearance of having been pro- 
duced by the wet collodion process. Sediment 
sometimes appears on the film after washing, 
particularly when over-developed, and gives the 
plate a fogged appearance; it may be removed, 
before drying, with a pad of cotton wool. 

A positive on a ferrotype plate is sometimes 
used by artists as a means of tracing from. 
Where a photograph is not to the correct scale 
a positive enlargement can be more rapidly made 
than a negative and print. As the image is. 
reversed in relation to right and left, it becomes. 
correct when traced over on gelatine by scratch- 
ing the outline with a needle-point and filling 
with blacklead or other set-off powder, the gela- 
tine being then turned over and rubbed down on 
to drawing paper or Bristol board, 


Ps ant 


ia geol 


AHdVYVOLOHd AdVOSAYS GNV UdVOSVAS 
WHYOLS V YaLdV 


Ferrous Acetate 


FERROUS ACETATE (Fr., Acétate de fer; 
Ger., Ferroacetat) 

Synonyms, ferric protoacetate, acetate of iron. 
Soluble in water. Fe(CH,COO),. Molecular 
weight, 174. It occurs as green crystals, and is 
obtained by dissolving iron in acetic acid. It 
was occasionally used in the wet plate days, 
and was then formed in solution by adding 
lead acetate to ferrous sulphate, when ferrous 
acetate was formed and lead sulphate pre- 
cipitated. 


FERROUS AMMONIUM SULPHATE (Fr., 
Sulfate de fer ammoniacale ; Ger., Schwe- 
felsaures Eisenoxydulammoniak) 

Synonyms, ammonio-ferrous sulphate, Mohr’s 

salt. FeSO, (NH,), SO,6H,O. Molecular weight, 
392. It takes the form of pale bluish green 
crystals. It is made by crystallising ferrous 
and ammonium sulphate. It was used in the 
old wet plate days as being a more stable salt 
than the ordinary ferrous sulphate. Seven parts 
of the double salt are equal to five of the ferrous 
sulphate. 


FERROUS CHLORIDE (Fr., Protochlorure de 
fer ; Ger., Eisenchlorid) 

Synonym, protochloride of iron. Fe Cl, 4H,O. 
Molecular weight, 199. Solubilities, 1 in 1-4 
water, soluble in alcohol. It is a greenish crys- 
talline salt, rapidly oxidised on exposure to the 
air into perchloride. It is made by dissolving 
iron wire in hydrochloric acid. It was suggested 
as a substitute for ferrous oxalate in the oxalate 
developer, and was occasionally used in the 
powder process. . 


FERROUS CITRO - OXALATE 
VELOPER 
A modification of the ferrous oxalate de- 
veloper suggested by Abney :— 


1.—Neutral potassium 


DE.- 


citrate . LG OF. 450 g 
Neutral potassium 
oxalate 24,, its. 
Distilled water to 20 ,, 1,000 ,, 
2.—Ferrous sulphate. 4 oz. 200 g. 
Distilled water to 20 ,, 1,000 ccs. 


For use, mix in equal parts. Cowan suggested 
the following, and it is especially suitable for 
gelatino-chloride plates, as any warmth of tone 
may be obtained by variation of exposure and 
developer :— 


1.—For cold tones : 
Neutral potassium 


oxalate. 1,200 gts, I25 g. 
Neutral potassium 
citrate : 400 ,, re Sn 
Distilled water to . 20 oz. 1,000 ccs. 
2.—For warm tones : 
Citric acid 3,200 grs. 333 g 
Ammonium carbon- 
ate. ‘ BADD 43 250.5 
Distilled water to . 20 oz. 1,000 ccs. 
3.—For extra warm tones: 
Citric acid 4,800 gts. 500 g. 
Ammonium carbon- 
ate. P ¥ 600 25 166)", 
Distilled water to . 20 oz. 1,000 ccs, 


16 


241 


Ferrous Oxalate Developer 


4.—Iron solution : 


Ferrous sulphate . 64 oz, 333 2. 
Sulphuric acid aie: sae T2°0. SCA. 
Distilled water to 20 ,, 1,000 


3 
For use, add 1 patt of No. 4 to 3 parts of 
Nos. I, 2 or 3. 


FERROUS NITRATE (Fr., Azotate ferreux ; 
Ger., Salpetersaures E1senoxydul) 
Synonym, protonitrate of iron. Fe(NO,), 
18H,O. Molecular weight, 536. Solubilities, 1 
in 6 water, soluble in dilute alcohol. It occurs 
as greenish white crystals. It may be prepared 
by dissolving iron wire in nitric acid, but the 
usual method is to mix 19 parts of ferrous 
sulphate with 36 parts of barium nitrate in 
solution, which gives 26 parts of ferrous 
nitrate. It was used in the wet collodion 
days, and gives an image much whiter in 
colour than does the ferrous sulphate. 


FERROUS OXALATE (Fr., Oxalate ferreux ; 
Ger., Eisenoxalat) 

Synonym, oxalate of iton. FeC,0;2H,0O. 
Molecular weight, 180. Practically insoluble in 
water, but soluble in alkaline oxalate solutions. 
Prepared by decomposing ferrous sulphate with 
oxalic acid, but generally obtained by mixing 
potassium oxalate and ferrous sulphate, in the 
form of ferrous potassium oxalate. 


FERROUS OXALATE DEVELOPER 

One of the oldest developers for plates and 
bromide papers, announced in 1877 simultan- 
eously by Carey Lea and Willis, of America and 
England respectively, now almost entirely re- 
placed by the newer organic developers. It has 
the great advantage of giving an image in pure 
metallic silver—that is, without any oxidised 
stain which is so often the defect of the newer 
developers; but, on the other hand, it oxidises 
rapidly, and gives in hard water a precipitate 
of oxalate of lime. Also, it raises the inertia 
of the plate, or, in other words, it does not bring 
so much out of a plate as do the newer developers, 
In the case of bromide papers, it is necessary to 
use an acid bath after development in order to 
ptevent the deposition of basic iron salts in the 
fibres of the paper; and this disadvantage has 
led to its disuse. It can be prepared most con- 
veniently by double decomposition between 


potassium oxalate and ferrous sulphate. The 
following may be considered a _ standard 
formula :— 
1.—Neutral potassium 
oxalate Pies -e 250 g, 
Distilled water to 20 ,, 1,000 ccs, 
2.—Ferrous sulphate. 6} 02. 330 g. 
Distilled water to 20 ,, 1,000 ccs, 
Pure sulphuric acid 10 mins. i.e. 


For use, add 1 part of No. 2 to 4 parts of No. 1. 
The iron must be added to the oxalate, and never 
vice versa, so that the oxalate is always in 
excess, because ferrous oxalate is insoluble im. 
water and soluble only in excess of an alkaline 
oxalate. The developer is a deep orange solu- 
tion which does not keep well. Another method 
of making it is by heating the oxalate solution 
to boiling point and adding dry ferrous oxalate 
until saturated, and then cooling and bottling ; 


Ferrous Oxalate Intensifier 242 


but the first method is preferable. Bromides 
can, of course, be used as with any other deve- 
loper, and the addition of a very small quantity 
of “ hypo,” 06 per cent., acts as an accelerator. 


FERROUS OXALATE INTENSIFIER 

In this process of intensification the nega- 
tive, after bleaching in mercuric chloride, is 
blackened by the application of the ferrous 
oxalate developer, which reduces the white 
silver and mercurous chloride image to metallic 
silver and mercury. The advantage of this 
process is that any amount of density may be 
obtained by repeating the bleaching and blacken- 
ing, each repetition adding more mercury, and, 
so far as is known, the image thus obtained is 
quite stable, and there is no selective action 
either in the high lights or shadows. It is 
important to wash thoroughly, preferably in 
water acidified with hydrochloric acid, after 
bleaching and before blackening. J. Chapman 
Jones recommends bleaching the well washed 
negative in a cold saturated solution of mercuric 
chloride to each ounce of which one or two 
drops of strong hydrochloric acid have been 
added. Afterwards, the negative is washed for 
one hour, blackened with a developer composed 
of 6 parts, by measure, of a saturated solution 
of potassium oxalate and 1 part of a saturated 
solution of ferrous sulphate. 


FERROUS POTASSIUM OXALATE (Fr., 
Oxalate de potassium ferreux; Ger., 
Kalium-Etsenoxalat) 

Synonym, potassio-ferrous oxalate. K,Fe 
(C,0,)2H.O. Molecular weight, 328. Obtained 
in the ferrous oxalate developer by the admix- 
ture of ferrous sulphate and potassium oxalate. 
If the sodium salt is used, ferrous sodium 
oxalate results. 


FERROUS SODIUM OXALATE (See the 
preceding article.) 


FERROUS SULPHATE (Fr., Sulfate de fer; 
Ger., Schwefelsaures Eisenoxydul) 

Synonyms, sulphate or protosulphate of iron, 
gteen copperas, green vitriol. FeSO, 7H,O- 
Molecular weight, 278. Solubilities, 1 in 1°8 cold 
and -s boiling water, insoluble in alcohol, It 
occurs as large bluish green crystals, efflorescent 
in air, obtained by treating iron wire with dilute 
sulphuric acid. It is used as the developer for 
wet collodion plates and to prepare the ferrous 
oxalate developer. On exposure to air it becomes 
oxidised and covered with a rusty powder of 
basic sulphate, which should be rinsed off before 
the crystals are dissolved. 


FERROUS SULPHATE DEVELOPER 

A developer used for wet collodion plates, 
of which the following may be considered a typical 
formula :— 


Ferrous sulphate ea 5O ges 40 g: 
Glacial acetic acid . 310 mins. 30 ccs 
Alcohol . : SEE CS SO ar, 
Distilled water to 20 OZ. TOC a ites 


A great many additions have been recom- 
mended, such as copper or magnesium sulphate, 
sugar, glycerine, albumen, etc., all of which are 


Field Camera 


supposed to have some special advantage. The 
development of a wet plate differs from that of 
a dry, in that it is what is termed “ physical 
development’; that is to say, the latent image 
itself is not developed, but the silver nitrate 
adherent to the film is reduced by the ferrous 
sulphate and deposited in situ on the. latent 
image, so that the growth of the image is from 
the top and not from the bottom or in the film, 
as with the chemical development of a dry plate. 


FIELD CAMERA (Fr., Chambre de touriste, 
Chambre de voyage, Chambre portative ; 

Ger., Reisekamera, Landschafts-kamera) 
Field cameras are necessarily designed to 
obtain the maximum of compactness and the 
minimum of weight consistent with steadiness, 


TENGE 


i 
i 


Since they will be more exposed to atmospheric 
and climatic influences than indoor cameras, 
the workmanship must be good, and the wood of 
excellent quality and well seasoned. Rigidity is 


of great importance. When extended, there 


should be no shake or looseness at either front 
ot back if grasped firmly with the two hands. 
The choice of pattern depends somewhat on the 
nature of the work to be undertaken. 

For technical, engineering, and suchlike pur- 
poses, a square bellows camera of somewhat 
heavy construction is usually preferred. Illus- 
tration A shows an apparatus which can be 
used in the studio or on a-tripod outdoors. 
The rigid front is suited for carrying heavy 
lenses, while the bellows racks backwards from 
the front, a useful movement in wide-angle work, 
where part of the image is sometimes liable to 
be cut off by the projecting baseboard of the 


f \ 
An 1 HE 
Kiar : 6 


\ 
Ct IN ium Bae ba TA 


a Mgt 
Se 


B. Tapering-bellows Field Camera 


ordinary type of camera. The back focusing 
movement is also valuable in photographing 
small objects at close quarters. The baseboard 
folds over the focusing screen when closed, thus 
preventing it from getting broken, 

A lighter, yet still substantial, type of camera, 
suitable for general work out of doors, is illus- 
trated at B. The swing front is useful when 


ee ee, ee 


A = 


Field Camera 


photographing high buildings, and a sufficient 
amount of rise is also provided for. The back, 
which can be swung either horizontally or vertic. 
ally, is arranged to slide close up to the front 
if desired, for use with wide-angle lenses. A 
well-known camera, noted for its great range of 
movement and particularly adapted for archi- 


a 


ia 


b = 
Sx 


C. Field Camera with Extreme Rise of Front 


tectural photography, is shown at C. The back 
and front may be swung in every imaginable 
position with ease, and at once rigidly clamped 
or locked. The extreme high rise of front will 
be noticed. The front not only rises and falls 
by rack and pinion, but may be moved horizon- 
tally or diagonally by means of a compound 
sliding and revolving device. 

A representative example of a moderate priced 
triple-extension camera is illustrated at D. A 
triple extension allows the bellows to be racked 
out to about three times the focal length of the 
average lens used with a camera of a given size, 
and is an invaluable feature when using long- 
focus lenses. 

The cameras above mentioned are illustrative 
of the chief tendencies of design in modern field 
apparatus. A notable advance is shown on 
earlier ideals of construction, especially with 
regard to lightness, compactness, and the pro- 
vision of mechanical conveniences. Double 


Me ny ed iy 
——— Fe ea a EAN he df, he 


D. Triple-extension Field Camera 


SS 


= 


book-form dark slides are usually preferred with 
field cameras, and they should work without 
either stiffness or looseness. (See also “* Camera,” 
** Dark-slide,” etc.) 


FIELD, DEPTH OF (See “Depth of Defini- 
tion, etc.’’) 


243 


Figure Studies 


FIELD LENS 


The lower lens of a microscope eyepiece that 
receives the image from the objective, as ex- 
plained under the heading ‘‘ Eyepiece.”’ 


FIELD OF LENS 


The imaginary surface at which the sharpest 
image that can be given is formed. With a 
theoretically perfect lens, this would be a plane, 
but in practice the field is usually concave, 
occasionally convex, and in the case of most 
anastigmats, plane with an annular depression 
at a considerable distance from the centre. In 
the theoretically perfect field all the rays, axial 
and marginal, come to a focus on a plane 
which is at right angles to the axis of the lens. 
This condition is fulfilled by one or two of 
the modern anastigmats, especially those made 
for copying. The most ordinary type of field 
is concave, the concavity being away from the 
lens. Before the introduction of the special 
Jena glasses, this was considered normal, in 
fact, inevitable, for so eminent an optician as the 
late Bing © Dallmeyer stated that a lens having a 
perfectly flat field “ does not exist, and cannot 
be made.” The amount of curvature of field 
varies greatly in different types of lenses, being 
most pronounced in portrait lenses of large 
aperture, less in single landscape lenses, and 
least of all in well-constructed rapid rectilinears. 
Other things being equal, it will be found that 
separating the elements of a double combination 
lens has a tendency to flatten the field, at the risk 
of increasing the astigmatism present; while in 
the case of single lenses the curvature is reduced 
to a minimum by placing the diaphragm as far 
as practicable from the lens. The field of a 
typical anastigmat is flat in the centre for a con- 
siderable distance from the axis, then comes a 
“dip” and then a recovery to almost the original 
plane. A field that is convex towards the lens is 
rarely found in practice, generally occurring in 
modern anastigmats which have been slightly 
over-corrected for flatness in the endeavour to 
attain other qualities. 


FIGURE STUDIES 

Portraiture is mainly directed to securing a 
“likeness,” while figure studies are generally 
intended to show character, costume, occupation, 
and so on. Renderings of figures in homely 
surroundings, or engaged in somewhat humble 
everyday occupations, are generally classed as 

‘genre.’ The great thing to avoid in successful 
figure work is any suggestion of posing or of 
camera-consciousness. Sometimes figures are 
dealt with as what may be called character 
studies, in which case care must be taken that 
position, lighting, view-point, and general treat- 
ment are all directed to securing the particular 
characterisation desired. In other cases the 
figures, singly or collectively, are treated in 
“settings,” or surroundings suggestive of their 
habits and employments. Whatever their occu- 
pation, work, or play, they should appear 
natural, and not suggestive of merely perform- 
ing for ‘the occasion. This does not imply that 
a certain amount of posing and arrangement 
must not be resorted to, but that there should be 
no evidence of such. 

In the case of character studies, careful observ- 


Figures in Landscapes 


ation of the subject is necessary to realise pre- 
cisely what is to be rendered in each particular 
case. Study is also equally essential where 
occupation is to be suggested. There are cer- 
tain poses and movements that are more effec- 
tive and suggestive than others, and these must 
be watched for and noted. ‘The sweeping move- 
ments of a mower, for example, cannot be shown 
completely, but the “ arrested motion” should 
be suggestive of action and not of a stationary 
pose. A blacksmith with his hammer poised in 
the air is more suggestive of energy and force 
than if his hammer is resting on the hot iron. 
In every such case the most characteristic 
position must be diligently sought for. The 
human interest always makes figure studies 
attractive, but it is extremely difficult to secure 
unqualified success without careful observation 
and- continued practice and experience. It is, 
in fact, a branch of photographic work that 
demands special aptitude, but one that well 
repays the utmost care that can be devoted 
to it. 


FIGURES IN LANDSCAPES 


There are some landscape subjects that appear 
quite complete without figures of any kind; in 
fact, in some cases, the introduction of the 
smallest figure would be detrimental. Frequently, 
however, a landscape without figures gives the 
impression of a mere setting—an empty stage. 
It has been said that in a perfectly composed 
landscape there is one, and only one, correct 
position for a figure or figures. It is, in fact, an 
exceedingly dificult matter to introduce figures 
into a landscape with complete success. They 
must be neither too prominent so that they 
attract undue attention, nor too insignificant 
so that they fail to take their place in the com- 
position. Above all, the figures must be appro- 
priate to their surroundings; they must not 
only be in the picture, but of it. 

The relation which figures bear to the land- 
scape varies. They may be so unobtrusive as 
merely to convey a necessary suggestion of life, 
or they may be so prominent as to claim more 
attention than the actual landscape. In the 
latter case, they are rather figures with land- 
scape, although the landscape is an important 
integral part of the whole picture. When several 
figures are included they should not be scattered 
indiscriminately, but should bear some relation 
to each other as well as to their surroundings. 
To this end it is helpful to study the character, 
placing, and arrangement of figures in land- 
scapes by good artists, and also carefully to 
examine photographic examples in which figures 
have been satisfactorily introduced. 


FILIGRANE 

A photographic process for water-marking 
paper, invented by W.B. Woodbury. A gelatine 
relief of the design is made by the Woodbury- 
type process, and when thoroughly hard and dry 
is passed through a rolling press with the paper 
to be water-marked. The result is that the 
paper is pressed thinner in some parts than in 
others, the thin parts appearing much lighter. 
On holding the paper up to the light a water- 
marked image is seen. The relief can be used 
a large number of times. 


ZA Film 


FILM (Fr., Pellicule ; Ger., Film) 

This term is applied to the surface which 
carries the sensitive silver salt: thus the film 
side of a paper or plate (Fr., Pellicule ; Ger., 
Schicht); but it has also become very generally 
applied to distinguish any flexible support from 
glass plates. The subject of flexible supports 
can for historical purposes be most readily 
dealt with by dividing it into the following 
classes: (1) negative paper; (2) stripping 
films; (3) cut films; (4) roll films. 

Negative paper was, of course, one of the 
first forms of negative material, and was intro- 
duced by Fox Talbot, in 1839, who also sug- 
gested making the finished negative more trans- 
lucent by waxing it. Le Gray, in 1854, intro- 
duced the wax paper process, in which the 
paper was waxed prior to sensitising. In 1849, 
Fox Talbot and Malone took out a patent for a 
resin-coated paper which was used by Newton 
in 1850, Le Gray in 1852, and Tillard in 1854. 
Crawford in 1854 used collodion-coated paper, 
and Geoffray in 1856 impregnated paper with 
rubber solution, fastened it to a glass plate 
coated with glycerine, coated it with colledion, 
and afterwards stripped it. Corbin in 1858 used 
collodionised paper; and Marion in 1863 also 
used dry collodion paper. Laoureux in 1878 
used a wax paper, which was rubbed with 
French chalk, coated with collodion according 
to the bath process, and the fixed negative was 
squeegeed down to a sheet of gelatinised glass 
whilst still damp, allowed to dry, and then 
stripped from the glass. In 1879, Ferrier, of 
Paris, patented a film of collodion and gelatine, 
and in the same year Stebbing introduced 
gelatino-bromide films on a hardened gelatine 
skin, Palmer, of Liverpool, in 1881 produced 
a film of gelatine and oxgall. In 1882 Morgan, 
of Morgan and Kidd, introduced negative paper, 
and Warnerke in 1884 made paper coated on 
both sides with emulsion, so as to avoid the 
curling of the paper and negatives. In 18385 
Woodbury and Vergara utilised a paper made 
transparent with resins, etc.; and ordinary 
negative paper was produced by Wilde, of 
Gorlitz. Eastman in 1885, Moh in 1898, 
Iumiére, the Thornton Film Co., in 1900 
(paperoid films), and Gaedicke in 1889, used 
thin varnished tracing paper. 

Stripping films were made by Milmson in 
1877, Ferran and Pauli in 1880, Thiebault in 
1886, Wilde in 1887, Moh in 1898, Balagny in 
1898, Hofmann in i901, Goldbacher in 1901, 
the Thornton Film Co. in 1901, and Wellington 
in 1901. In all these the paper was prepared 
either with a soluble gelatine film, or wax, 
tubber, or resin, which allowed the finished 
negative to be stripped from the paper sup- 

ort. 

; Cut celluloid films were first suggested by 
Fourtier (France) in 1881, but Carbutt (U.S.A.) 
seems to have been the first to introduce them 
commercially in 1888, though he had made some 
in 1884. In 1882 Pumphrey (Birmingham) 
introduced a “flexible glass” support, consisting 
of gelatine and collodion, and Moh in 1890, 
and Raphael in 1892, used thin sheets of mica, 
Froedman in 1887 introduced a support of 
bichromated gelatine which had been rendered 
insoluble by exposure to light; Stebbing in 


Film 


1879 used a hardened gelatine film between two 
films of collodion; and Wilde in 1883 used 
insoluble gelatine and collodion. Balagny in 
1886 used alternate layers of collodion, varnish, 
and gelatine. In recent years most plate 
makers have produced cut celluloid films one- 
hundredth of an inch in thickness. 

Roll films seem to have been first suggested 
by Melhuish and Spencer in 1854, and by 
Merritt and Warnerke in England and Captain 
Barr in India in 1875. Barr was the first 
to suggest the present system of using a black 
material at the back of the film, which was 
continued beyond the ends of the sensitive 
material (then paper) to protect it from light. 
Roll celluloid films appear to have been con- 
ceived first by Goodwin (U.S.A.) in 1887, although 
the patent was not granted till 1898; while 
this patent was lying in the American patent 
office, Reichenbach, of the Eastman Kodak Co., 
applied for a similar patent, which, like Good- 
win’s, included the “‘non-curling” layer of 
gelatine on the back of the celluloid. Cody, of 
the Blair Camera Co., patented in 1894 the 
use of the now well-known daylight loading 
cartridge. Many of the manufacturers who are 
mentioned as making cut stripping films also 
prepared roll films, but the celluloid, about 
xvso in. thick, is now almost universally used. 

The treatment of films, as regards develop- 
ment and fixing, is precisely the same as for 
plates. The only point to which attention should 
be directed is the keeping power of the emulsion 
when this is coated on celluloid, and though 
this is generally recognised to be practically 
limited to twelve months after coating, instances 
have been recorded of films—especially cut films 
—being fit for use after five years. This possibly 
can be explained by the different state of dry- 
ness of the support. 

In process work, the word “film” is applied 
in several ways. There is the film obtained by 
stripping negatives. The “Lotus” film was 
introduced by Mawson and Swan to facilitate 
the obtaining, by stripping, of film negatives, 
these films being of hardened gelatine of sub- 
stantial thickness. 

The gelatine films known as “ Shading 
Mediums,” often simply called ‘“‘ films,” have 
lines, stipples, or patterns moulded on their 
surface, so that they can be inked and the 
pattern transferred by rubbing down with a 
stylus, or by pressure with a small rubber 
roller, 

The “Norwich Film” is a transparent gela- 
tine film grained on one side for drawing upon 
in pencil, crayon, or ink, according to the degree 
of fineness or coarseness of the grain. By making 
the drawing with a greasy ink the surface can 
afterwards be flowed over with a non-actinic 
alcohol soluble varnish, which will not affect 
the drawing. The latter can then be washed 
away with turpentine, leaving the lines or granu- 
lations transparent, so that the film becomes a 
negative which can be printed from by any 
photographic process. If the film is drawn on 
with lithographic crayon or lithographic transfer 
ink, the drawing may be transferred in the usual 
lithographic manner by damping. the gelatine 
and running through a press in contact with 
stone or zinc. 


245 


Film Manipulation 


FILM CAMERA (Fr., Chambre a pellicule; 
Ger., Filmkamera) 


In its primary sense, a camera specially de- 
signed for use with films, whether flat or in the 
roll. Such cameras are mostly of the hand type, 
and typical examples of the various kinds will 
be found under the heading ‘‘ Hand Camera.” 
Any ordinary camera may, however, be used 
with films by the simple expedient of employing 
a roll-holder instead of a dark-slide; or, if flat 
films are preferred, a suitable changing box, 
adapter, or film pack may be used. 


FILM CARRIER (Fr., Porte-pellicule ; 
Filmrahmen) 

A kind of sheath, usually of thin metal 
turned over at the edges on three sides, used for 
holding flat films in dark-slides or in hand 
cameras. Some carriers are indented from the 
back so that the film is kept close to the front, 
in order to be in register with the focusing screen ; 
others require the insertion of a piece of black 
cardboard between the film and the carrier. 
Another type of carrier consists of a flat metal 
back over which folds a hinged frame. The film 
is laid on the back and the frame closed down 
on it, securing itself by a clip at the edge. 

The term film carrier is also sometimes applied 
to roll-holders and adapters for holding films. 


FILM HARDENERS (See ‘“ Hardeners.’’) 


FILM HOLDER (Fr., Pince a pellicule ; Ger., 
Filmshalter) 


A metal or wooden clip used to hold the ends 
of roll films when developing in the length. 
Another kind consists of a flat piece of metal 
turned over at two edges, to hold a short por- 
tion of film, cut from the length, flat during 
developing. The term film holder is also some- 
times given to the roller slide, or roll-holder 
(which see). 


FILM MANIPULATION 

The use of films, both flat and rollable, has 
become during recent years more and more 
popular, and there has been much discussion 
as to whether these or plates are the more 
advantageous, although, results alone con- 
sidered, there is no difference between them. 
The developers, fixers, intensifiers, etc., suit- 
able for dry plates will suit films also, for the 
reason that the emulsions are the same although 
the support is glass in the first case and cellu- 
loid in the second. 

Flat Films.—Flat films are treated exactly 
as though they were plates. There may be 
difficulty in keeping them wholly immersed 
in the solutions, on account of their buoyancy, 
which tends to make them float on the surface 
of the liquid, thus leading to uneven develop- 
ment, markings, and yellow stains. It is best 
first to place the required amount of developer 
in a dish and to slip the film face upwards into 
it well under the surface; or the film may be 
placed in a dry dish and the developer poured on. 
By rocking the dish the film is kept on the 
move, and the developer made to flow evenly 
over it. Some workers use a narrow wooden 
frame A, which tightly fits the bottom of the 
dish; the film is then pinned face upwards to 


Ger., 


Film Manipulation 246 


the frame and the developer poured on. But 
this method ought not to be necessary except 
that films tend to curl very much when wetted. 
The disadvantage of using a false bottom entirely 
of wood is that unless it fits very tightly in the 
bottom of the dish it may float on the surface 
and do more harm than good. 

Cutting Roll Films.—Only when roll films are 


Film Manipulation 


threaded, the whole length of film being worked 
backwards and forwards through the developer, 
which should cover the bars. In a contrivance, C, 
embodying the same principle, a bent rod carries 
a roller acting as a bar to keep the film under 
the developer; with both these contrivances it 
is necessary to hold one end of the strip in each 
hand after the manner shown at F. A con- 


ing Dish 


bars. 


unrolled in a proper way is there little or no 
danger of cutting through the images. The 
cutting up of a roll film before development is 
necessary only when each exposure is to be 
developed separately, after the manner of flat 
films. D shows the proper and E the improper 
method of cutting up a roll film. The roll should 
be held in the left hand and the end of the 
wound-up film pulled with the right, the black 
paper being on the top and the film beneath. 
Only one number should be unwound at a time, 
and when the division marks at the edges are 
seen (between the numbers), the film is placed 
in contact with the black covering paper and 
both cut through evenly with a pair of scissors ; 
by this method the paper and film are in con- 
tact and in agreement as in the camera. The 
wrong way of cutting up a film (see E) is to bring 
the loose white film to the top of the black 
paper, because when this is done the images 
will invariably be cut through, as the division 
markings will not be true. The film must be 
swung round below the paper, in the direction 
shown by the dotted lines. 

Developing Roll Films.—The object of cutting 


D. Proper Method of Cutting Film 


up films is to avoid the awkward operation of 
developing them in the strip form. With the 
shorter lengths there is, however, no difficulty 
in developing them whole, but when longer than 
36 in. it is better to cut them up or to use one 
of the numerous film-developing devices on the 
market, which, of course, are suitable for the 
shorter lengths also, At B is shown a dish 
having two cross-bars, under which the film is 


A. Frame to fit Develop- 
B. Dish with Two Cross- 
C. Dish with Roller 


ptf 


trivance on a different principle is shown at G; 
one end of the film is attached to a spring 
drum, which is made to revolve, and the film 
passed through the developer by alternately 
pulling and slackening the other end. These 
and other accessories are very convenient, but 
in their absence the following method may 
be adopted. A dish is filled with the developer. 
The whole length of film is detached from the 
black paper, one end is taken in each hand, and 
the film is passed, sensitive (matt) side down- 
wards, through the developer, a see-saw move- 
ment of the arms being maintained, and the film 
passed to and fro through the developer until 
the whole series of images is fully developed. It 
is a good practice to develop the whole strip 
until the barest outlines are visible, and the 
spaces dividing the pictures can be distinctly 
seen; the film can then be cut with scissors, the 
partly developed pictures placed in cold water, 
and each one developed separately in an ordinary 


E. Incorrect Method of Cutting Film 


flat dish. It is advisable to keep the partially 
developed films on the move while in the water, 
as, if allowed to stand, they may remain curled 
up or on the surface, in which case markings and 
stains would appear. 

Fixing.—Films may be fixed in the strip, or cut 
up. Even if the film is developed in strip form, 
it may be advisable to cut it up before or during 
fixing, for the sake of convenient handling; but 


1 
‘ 
; 


Film Manipulation 


opinions differ on this point. Films need more 


care than plates when fixing, because, should the 
films float on the surface of the fixer, exposure 
to the air will cause markings, yellow stains, etc., 
which cannot easily be removed. An acid fixing 


H. Film held in 
Cork Clip 


F, Developing 
Film 


bath (potassium metabisulphite and “ hypo ’’) 
is better than an ordinary fixing bath of plain 
“hypo,” as the metabisulphite prevents stains. 

Washing and Drying.—Films cannot be washed 
and dried in a rack like plates, and some trouble 
is often met with in keeping them under the 
surface of the water. Numerous devices have 
been introduced for washing films properly. A 
useful contrivance is shown at H; a cork is cut 
in halves lengthways, after cutting a notch in 
the top; then an indiarubber band is placed 
around the halves as shown, the whole now 
forming aclip. The film is inserted in the cork, 
which will float on the surface of the water and 


UCT i 
“il 


I. Films Pinned up to Dry 


Y 


hold the film beneath the surface. Films are 
best dried by pinning them, face (emulsion sur- 
face) outwards, to a shelf, as shown at I, or 
special clips may be used in place of pins, All 
fiat films should be kept under slight pressure 
when not in use. If a film is stored in a roll, it 


247 


Film Stripping 


should always be wound sensitive surface outside, 
as it will then lie flatter when printing. Films 
are better varnished, and for wet films a borax 
and gum lac solution is best, but for dry films a 
dammar varnish may be used. (See ‘“ Varn- 
ishes.”’) By the aid of special tanks, the develop- 
ment of films may be carried out in daylight. 


FILM PACK 

A device for exposing a number of cut films 
successively. A holder, somewhat similar to a 
dark-slide, is loaded with a packet of cut films, 
This can be done in daylight. Projecting from 
the packet are paper tabs, and by pulling these 
out and tearing them off the films are successively 
brought into position for exposing, and then 
carried round to the back of the pack. When all 
the films have been exposed, the pack may be 
removed from the holder (still in daylight), and 
a fresh one substituted. This provides a con- 
venient means of exposing an indefinite number 
of cut films without having to resort to a dark- 
room. Some cameras are made for using a film 
pack only, in which case the holder is usually 
an integral part of the camera; but the holder 
or adapter is also suitable for use on other 
cameras interchangeably with dark slides. A 
special tank has been devised for the develop- 
ment of cut films as used in the pack, although, 
of course, its use is a convenience rather than a 
necessity. 


FILM SHEATH (Fr., Etui a pellicule, Porte- 
pellicule ; Ger., Filmscheide, Filmrahmen, 
Blechrahmen) 

A metal sheath for holding flat films in maga- 
zine hand cameras; practically identical with 
certain forms of film carrier (which see). Ordin- 
ary plate sheaths may be used for films if a 
piece of black cardboard is inserted behind each 
film. In some patterns of hand cameras, the 
changing mechanism is designed for use with 
sheaths of a definite thickness, and will not work 
with thinner sheaths. 


FILM STRIPPING 

Films may easily be stripped from their glass 
supports and transferred as required, this course 
often being necessary when the glass of a nega- 
tive is cracked and the film is undamaged. In 
reversing a negative for single transfer carbon 
or collotype work, the stripping method is also 
useful. If desired the film may be enlarged in 
course of transference, as described under the 
heading ‘‘ Enlarging by Stripping.’ In cases 
where it is not desired to enlarge the film, the 
hydrofluoric acid used for stripping must be 
diluted with methylated spirit, which, to some 
extent, counteracts the tendency to expand. 
The following is suitable :-— 


Methylated spirit . 5 oz. 1,000 ccs. 
Water : . I$ drms. 27h toas 
Glycerine : Moh eae S7Sh 
Hydrofluoric acid 1—14 ,, 25—37°5 ,, 


Make this up without the acid and keep as a 
stock solution, adding the acid just before 
using. The negative to be stripped should not 
have been varnished, or, if it has been, the 
varnish must be removed before treatment. It 
should be noted that hydrofluoric acid attacks 


Film Stripping 


glass, and any mixture containing the acid must 
therefore be kept in an indiarubber or ebonite 
cup or dish, or in a glass vessel that has been 
coated internally with paraffin wax (the wax is 
melted, poured in and out again, leaving a coat- 
ing on the sides). Some sheets of waxed paper 
are also needed before the work of stripping can 
be begun, also a glass plate coated with gum or 
gelatine on to which the film is to be transferred, 
for owing to the use of a large proportion of 
spirit the removed film will not adhere to plain 
glass. Lay the negative to be stripped on a 
perfectly level surface, and with the aid of a 
straightedge, and by means of a sharp penknife, 
cut through the film to the glass at } in. from 
the edge all round; then pour enough of the 
stripping mixture on to the film and spread over 
evenly with a camel-hair brush, or a piece of 
paper or cotton-wool. In about five minutes 
the film will become loose, and the narrow bands 
of film at the edges may be stripped away, this 
being a good test as to how the stripping mixture 
is working on the film. If after five minutes the 
film refuses to move, a little more acid may be 
added to some more of the solution, and spread 
over the film. No attempt must be made to 
hasten the loosening of the film at the edges by 
pulling; the acid must do all the work. When 
the margin comes away without the slightest 
resistance, it is a sign that the main film is in 
a State to be removed. A penknife may be in- 
serted under one corner of the film just to see if 
this will come away easily from the glass. The 
film being still on the plate, drain off superfluous 
acid, and pour on more of the stripping mixture, 
this time without the acid. This in turn is 
poured off, and a sheet of the waxed paper 
brought down upon the loosened film, and lightly 
squeegeed down. The film will adhere per- 
iectly to the waxed paper, and they can be 
removed together on to the new glass and 
squeegeed over lightly ; the paper is then pulled 
gently away, leaving the film upon the prepared 
lass. 

: When a reversal—as regards right and left— 
is wanted, the film on the original negative 
should be transferred to a plain piece of white 
paper covered with the spirit mixture minus 
the acid; the waxed paper is then laid over 
the removed film, and the two papers, with the 
film in between, squeegeed into contact; the 
papers are then separated carefully, in such a 
manner that the loose film remains on the waxed 
paper; it is then transferred to the prepared 
plate in the manner described above, care being 
taken to keep the film flat and in perfect contact 
with its support, 

Owing to objections to the use of hydrofluoric 
acid, many prefer to do without it, and they 
employ some such method as the following. The 
film is liable to slight enlargement, by about 
one-thirtieth of its length, which matters little 
if it has been cut round the edges in the manner 
already described. The negative is placed in 
the following bath :— 


Caustic soda 20 grs. 23 g. 
Formaline 20 drops 2I ccs, 
Water 4 OU 1,000 04, 


The formaline toughens the film, and in about 
ten minutes the film could, if it were desired, be 


248 


Filter Paper 


rolied back with the finger. But do not do so ; 
instead, when it appears to be loose, transfer to 
the following bath :— 


Glycerine - 60—70 drops 63—73 ccs. 
Hydrochloric acid . 50 eg S200) 
Water . ‘ . 2 @2. t000) i, 


in which it can be entirely detached, and as it 
floats in the liquid either side may be attached 
to the new glass. In order to ensure the film 
sticking to its new support, it is advisable that 
the following substratum should be applied to 
the glass :— 


Formaline : - 10 drops tien, 
Gelatine . : Me sss 4°5 g. 
Water ‘ ‘ 2 OZ. 1,000 ccs, 


Swell the gelatine in the water, dissolve by 
heating, and add the formaline; coat the glass, 
allow to dry, transfer the wet film to it, press 
down, and allow to dry naturally. A fixed 
and washed unexposed dry plate also serves as 
a support. 

Films are removed from celluloid supports by 
soaking in the caustic soda and formaline mix- 
ture already given, and then in the hydrochloric 
acid and glycerine bath; the films, slightly 
enlarged, are washed and transferred to glass 
or celluloid. 

A convenient method of using hydrofluoric 
acid for stripping is to manufacture it as 
required, which can be very easily done by 
making a solution of sodium, ammonium or 
potassium fluoride, about 10 grs. to the ounce of 
water (20 g. to 1,000 ccs.), and acidulating with a 
few drops of some strong acid, such as sulphuric 
or nitric, applying the mixture to the nega- 
tive. Hydrofiuoric acid is generated and strips _ 
the film, and the solution may be thrown away 
when it has done its work. The dry fluorides 
keep well in ordinary glass bottles. 


FILMOGRAPH (Fr., Filmographe ; Ger., Fil- 
mogvaph) 
The name given to an early pattern of film 
camera by Humphrey. 


FILTER (See “‘ Colour Screen or Filter.’’) 


FILTER PAPER (Fr., Papier a filtver; Ger., 
Filtrierpapier) 
Paper folded into a funnel for the purpose of 
filtering liquids. Practically only two kinds of 
filter paper are known to photographers, the 


Methods of Folding Filter Papers 


white and the grey, cut in circular form. They 
are sold in packets of one hundred, the size 
ranging from about 23 in. to 20 in., and the 
prices from about 3d. to 2s. 6d. per packet. 
There are many ways of folding such papers 


Filter, Vacuum 


into cones for fitting funnels, two of the most 
general being here illustrated. A shows the 
commonest style, the paper being first folded 
into halves and then into quarters; it is then 
placed in the funnel and one side opened out. 
In B the circle is first folded into halves and then 
laid flat again, leaving a crease to show the 
diameter. The ends of the diameter are then 
brought together and the halves opened out. 


FILTER, VACUUM 

A device by means of which liquid is forced 
through a filtering medium by atmospheric 
pressure. 

A simple form of filter for viscous fluids, such 
as the fish-glue solution used by process workers, 
is that shown at A. A strong glass flask of about 
one litre capacity has a nipple connection blown 
into its side near the neck. To this nipple a 
Sprengel “‘ pump ”’ of glass is attached by means 
of a rubber tube. The construction of the 
“pump” is shown at B. The inner tube is not 
continuous, but consists of two tapering tubes, 


A. Vacuum Filter 


B. Sprengel Pump 


one being sealed to the upper end of the outer 
tube and the other to the lower end, their tapered 
ends meeting and being enclosed one within the 
other for a short distance. The air drawn from 
the flask can thus pass between them. The 
vertical nozzle of the “ pump ”’ is connected with 
a water-tap. The rubber tubes must be tightly 
bound on, or they will be blown off by the pres- 
sure. The funnel containing the filtrate is 
thrust through a rubber bung placed in the neck 
of the funnel, and it is desirable to have a per- 
forated porcelain plate in the funnel to prevent 
the filtering medium, which may be cotton-wool, 
glass-wool, or felt, being sucked down the neck 
of the funnel. The filtrate having been poured 
in, the water-tap is turned on and the rush of 
water through the “‘ pump” draws the air out 
of the flask, creating a vacuum init. Thus the 
filtrate is powerfully sucked through. It is 
desirable to have a clip on the tube leading from 
the flask to the “‘ pump,” so that the tube can 
be pinched when the water is turned off, or the 
water in the tube will be sucked back and dilute 
the filtered liquid. 


FILTRATION (Fr., Filtration; 
trierven) 

A process used to remove from a liquid or 
solution any insoluble extraneous matter, 
Usually an unsized, pure,;porous paper is used, 
(See “Filter Paper.’’) For ordinary purposes 


Ger., Fiul- 


249 


Finger-print Photography 


a small tuft of absorbent cotton-wool stuffed 
into the neck of a funnel will usually suffice. 
For filtering emulsions well-washed swansdown, 
or a felt filtering bag, may be used. It should be 
noted that developers should only be filtered— 
or strained, to use a more correct term—through 
loosely packed wool, otherwise they may oxidise. 
Glass-wool (finely spun threads of glass) is used 
for filtering collodion or corrosive liquids which 
would attack paper or cotton-wool. 


FILTRATION, UPWARD 


A method of filtration which it is convenient 
to adopt in the albumen process. A _ glass 
cylinder, open at both ends, has two thicknesses 
of washed muslin tied over one of the ends. 
The albumen is placed in a vessel slightly larger 
in diameter than the cylinder, and the latter is 
then lowered into the vessel, muslin end down- 
wards. The weight of the cylinder forces the 
albumen solution to pass upwards through the 
muslin into the cylinder. 


FINDER, VIEW (See “ View Finder,” “‘ Direct 
Finder,’”’ ‘‘Iconometer,”’ etc.) 


FINGER - PRINT PHOTOGRAPHY 
Photographie @ marque de doigt ; 
Fingerspur Photographie) 

The photography and systematic registration 
of finger-prints has become of immense import- 
ance in the detection of crime. The methods 
employed may be divided into two classes: (1) 
those used when the individual whose finger- 
prints are to be examined or registered is pre- 
sent to give more or less voluntary assistance ; 
and (2) those in which the finger-prints have been 
involuntarily left behind by their originator. 
The procedure adopted at New Scotland Yard 
under the first circumstances is very simple. The 
best black printers’ ink is spread in a thin, even 
film on flat tin-plate or copper by means of a 
roller. The finger to be recorded is pressed 
down lightly and steadily on the film of ink, 
taking care not to move it sideways at all. After 
a few seconds the finger is raised and pressed 
down on a smooth white card or paper, when a 
sharp, clear impression should result. This is 
known as a “‘ plain’”’ impression. Another kind 
is obtained by placing the bulb of the finger on 
the inked slab, facing to the left, and turning 
it gently over until it faces to the right. The 
finger is then pressed gently on the paper, roll- 
ing it from left to right as before, thus making 
what is called a “‘ rolled’ impression. With an 
unwilling subject, trouble may arise from the 
finger being deliberately moved. 

For experimental work, a good substitute for 
the above method is allow a drop of printing ink 
to fall on a smooth card or glass, and to spread 
it out with a finger. Finger-prints on white 
pane may be photographed on a photo-mechan- 
ical plate, giving a short exposure to secure 
contrast and developing with hydroquinone. 
Prints from the negatives may be made on gas- 
light paper. Another and quicker way is to have 
the inked finger pressed on a clean sheet of giass 
instead of on paper. Several thicknesses of 
gummed paper in strips are then stuck on the 
glass at the sides, and it is placed in a printing 
frame. In the dark-room, a slow, ordinary 


(Fr., 
Ger.; 


Finger-print Photography 


plate, backed, is laid film side downwards on the 
glass, the gummed strips serving to protect the 
film from the still wet ink. Having inserted the 
back and fastened the frame, an exposure of 
about half a second is given at two feet distance 
from a fish-tail gas burner. This may be done 
by turning down the gas to an almost invisible 
blue point, holding up the frame, and then 
turning the gas up and off as rapidly as possible. 
On development with hydroquinone a good 
sharp negative should be secured. The frame 
must, of course, be kept still. The prints here 
shown were obtained from negatives made in 
this way; A, B, Cc, and D are finger-prints, E 
and F being thumb-prints. a and B are from 
the same finger at different times; the lines will 
be found to tally, and the mark of a slight cut 
at x is plainly seen in both. 

If, however, the finger-prints have to be 
searched for patiently and carefully, and are 
eventually found in awkward places, on un- 


250 


Finishing Photographs 


Another class of finger-prints which call for 
great care, since the record is so easily disturbed 
and lost, are those in dust. If on a dark sur- 
face, these are readily photographed with a 
direct front lighting. When they occur on a 
window-pane or other colourless glass, a dark 
background should be placed at the back, a 
short distance away, and the light should come 
obliquely from behind. In rare cases semi- 
invisible finger-prints may sometimes be ren- 
dered conspicuous by chemical treatment, if 
there is any idea of the occupation of their 
suspected producer. Thus, for example, a 
tanner fresh from work might reasonably be 
expected to leave traces of tannin in his finger- 
prints, which, under favourable conditions, could 
be rendered black by treatment with a solution . 
of a ferric salt. 

It is found that a solution of silver nitrate, 
of say 6 per cent. strength, will occasionally 
cause the appearance of an unsuspected finger- 


SoS aN 
SS: SS 
ge SS 
GN 
Z ZY LEER Bas SASS 
WY ere? 
UG, Gone Wan : 

rt 4 bE 
Yi fa) DE AS 
( Oe AOR: F, Nay 
SE LY, Mh Uy 5 
Lh 2% yy, ee 
rege thee tg 
F 


Finger and Thumb Prints 


favourable surfaces, and in all probability faint 
and nearly invisible, the work becomes much 
more difficult. When trouble arises owing to 
any unusual colour of the ground on which the 
finger-print occurs, an orthochromatic plate 
must be used in conjunction with a suitable 
colour filter, to secure contrast, each case being 
treated, of course, according to its particular 
requirements. 

The majority of involuntary finger-prints are 
greasy ones. To photograph these, if on a light 
surface, such as china, enamelled furniture, etc., 
they should be dusted lightly with dry, finely 
powdered plumbago or graphite; a flat, broad 


camel-hair brush is charged with a little of the » 


powder, and, holding this a short distance above 
the finger-print, the handle is tapped gently 
with the forefinger of the disengaged hand. Or, 
instead, the hand holding the brush may be 
nudged or shaken. The surplus powder is care- 
fully blown away with a small bellows; on no 
account should the breath be used. Greasy 
finger-prints on a dark surface—old oak furni- 
ture or black ironwork, for instance—may be 
treated in the same manner, using, however, 
dry, finely powdered whitelead instead of the 
plumbago. 

Finger- prints in blood on a dark surface 
should be placed where there is no extraneous 
light, as in a cellar or dark room, and lit from 
the front with magnesium ribbon or the electric 
arc, of course screening the direct rays from 
the lens of the camera. 


print on ordinary paper, or will intensify a semi- 
invisible one. 


FINGER TIPS OR STALLS (Fr., Doigtiers ; 
Ger., Fingerlinge) 


Rubber sheaths, like the tips or fingers of 
gloves, worn when developing, working in wet 
collodion, sensitising with bichromate, etc., to 
protect the fingers from staining and as a safe- 
guard against the entrance of poisonous chemicals 
into cuts or wounds. 


FINISHING PHOTOGRAPHS 


Photographs are frequently finished with 
crayon or water-colour, and of recent years, 
the aerograph (which see) has been extensively 
employed for the purpose, this providing an easy 
means of introducing soft backgrounds. While 
details of the actual methods will be found under 
the heading ‘‘ Working-up Prints,’’ it may be 
said here that photographs to be finished by 
hand should be on matt paper, as otherwise the 
touching-up shows prominently. Ordinarily, the 
medium (generally water-colour) should match 
the tone of the print, but for photo-mechanical 
reproduction this is not necessary. The aim in 
finishing a photograph should be to strengthen 
or to modify as may be necessary, and not to 
introduce work that is not of a photographic 
character; this naturally forbids all outlining. 

In process work, many special considerations 
have their bearing upon the extent of the 


Firelight Effects 


finishing and the methods employed. Much 
information is given in the article under 
the heading “ Aerograph,” and further notes 
of a practical character will be found at 
* Working-up Prints,”’ 


FIRELIGHT EFFECTS 

Effects represented in photographs appearing 
to have been taken by the fireside and by the light 
of the fire. Firelight is too weak to illuminate 
the sitter for photographic purposes without an 
undue exposure, and artificial aids are necessary. 
Daylight is the most satisfactory light for the 
purpose, and the illustration shows the method 
employed by H. Essenhigh Corke. A suitable 
window is selected and blocked up with brown 
paper or other opaque material, leaving, how- 
ever, a space about 2 ft. square, the bottom of 
which should be level with the top of a table or 
platform arranged close to the window. ‘The 
light admitted by the space is the “‘ firelight,’’ 
but the space itself does not show in the photo- 
gtaph. A fender and hearthrug may be arranged 


Arrangement for Firelight Effects 


to make the deception more complete, loose tiles 
or wallpaper with a tiled pattern being placed 
in the fender. The sitter should be placed as 
near to the “fire’’ as possible, so that the 
light may be concentrated upon him. A dark 
background should be used. 

Firelight effects may be taken at night by 
the aid of magnesium. Throwing magnesium 
powder into a real fire is rarely satisfactory, 
and a better way is to use a magnesium lamp 
in an empty fireplace, firing the powder when all 
is ready for exposure. Any other lights in the 
room may be left on, as the average artificial 
light will do no harm. In some cases it will be 
advisable to use a weak supplementary flash 
in the room in order to assist the very deep 
shadows. If there is a good draught up the 
chimney no magnesium smoke will escape into 
the room and show in the picture, but if the 
draught is poor it will be well to fit a sheet 
of plain glass in the fireplace, in such a way as 
to trap the smoke. The finished print should 
be stained with an aniline dye of a suitable 
tint, so as to give it a firelight colour, and various 
experiments in toning may be tried. 


FIRES, PHOTOGRAPHING 

The domestic fire is an awkward thing to 
photograph satisfactorily, owing to the moving 
smoke and the non-actinic colour of the red-hot 


251 


Fish, Photographing 


coals, The best effects are obtained by allowing 
the fire to burn as bright and as smokeless as 
possible, and then scattering a little saltpetre 
on it. 

The photographing of conflagrations is, in 
daytime, no more difficult than ordinary land- 
Scape or architectural work, the only precaution 
necessary being, in addition to getting out of 
the way of firemen and water, to take up, 
if possible, a position on the windward side, in 
order that the smoke blows away from the 
camera and appears more or less as background. 
Large fires at night generally give out sufficient 
light to allow of brief exposures. 


FIREWORKS, PHOTOGRAPHING 


Fireworks really photograph themselves when 
once the camera is ready. A stand camera 
must be used, or a hand camera fixed upon some 
suitable support, as it is impossible to hold a 
camera in the hand still enough for the neces- 
sary exposure. The camera must be focused 
for what is known as “infinity’’; this is best 
done in daylight by focusing some distant object 
and fixing the camera at that focus or making a 
mark on the baseboard, so that the lens may be 
put in position at night when there is little or 
nothing to focus. When the firework display 
begins, the camera is set up in the required 
position, and the first few rockets looked at on 
the focusing screen in order properly to judge 
the correct position. The plate is then inserted 
and a time exposure given—a minute or more, 
as desired, or until a sufficient number of dis- 
charges has been obtained on the plate. Only 
one or two fireworks on a plate would look very 
mean, and it is better to get a good number of 
discharges, not interfering to any extent with 
one another. As large a stop should be used 
as possible, and a rapid plate, backed so as to 
prevent halation, although with small stops 


and slow plates some of the very bright rockets 


may be obtained. The curves taken by rockets 
in their ascent are very graceful, and care should 
be taken to get far enough away to include 
them when they are high and burst. The plates 
are developed as usual, care being taken not to 
under-develop, but to secure as much contrast 
as possible. Firework exposures frequently 
appear disappointing when in the developer, 
and the plate may seem to be slow in developing 
and to lack density, but such exposures gener- 
ally fix out well. Printing should be deep, so 
as to get a black background. 


FISH, PHOTOGRAPHING 

This is a branch of Nature photography offer- 
ing a field of peculiarly interesting work. The 
most important part of the outfit is a good stand 
camera, with a modern anastigmat, working at 
f/6. Isochromatic plates should always be used, 
where possible, in conjunction with a compensat- 
ing filter (isochromatic screen). The size of the 
aquarium or tank, in which the fish are to be 
placed for photographing, must necessarily be 
governed by the predominant size of the sub- 
jects. It is a great mistake to have too large a 
tank, for it will cause needless labour and trouble, 
but at the same time it must be kept in mind 
that unless the fish has ample room to move 
freely, it will become alarmed, and will certainly 


Fish-eye Camera 


assuine unnatural positions, while in its struggles 
to escape from its cramped surroundings it may 
injureitself. The photographic tank should have 
all four sides of glass, so as to admit as much light 
as possible, and one of the long sides must be of 
good “ patent plate” glass free from scratches, 
air-bells, and other blemishes, which would show 
in the photograph, as it is through this side that 
the photographs will be taken. This tank should 
be kept purely for photographic purposes, and 
not used as a regular stock aquarium, and must 
be kept perfectly clean inside and out. Cleanli- 
ness is most important. The water with which 
the photographic tank is filled should first be 
strained through a piece of linen, so that there 
are no floating particles. The fine shingle used 
for the floor must be well washed before being 
placed in the tank, to rid it of mud and fine 
sand. The plants must for the same reason be 
well washed ; their roots may be cut away, and 
the base of the stems weighted with a strip of 
soft lead folded round and embedded in the 
shingle. It is as well to place the plants rather 
towards the back of the tank, as otherwise they 
are apt to get in the way and partially obscure 
the subject to be photographed. The subject 
itself will generally be found to look all the 
brighter and better for a gentle sponging to clean 
off any dirt that has deposited in the natural 
slimy secretion with which the body may be 
coated. The photographic tank should be placed 
in such a position that as good top and side 
lighting as possible are obtained. The camera 
should be placed directly in front of and at the 
centre of the long side of the tank that is 
fitted with the “ patent plate.” This glass must 
be perfectly clean and free from smears. It isa 
good plan to keep a soft washleather specially 
for the purpose. Instead of introducing plants 
into the photographic tank, a plain tinted back- 
ground may often be used with advantage. If 
plants are used, care must be taken to select only 
those which would be found growing in the 
favourite haunt of the particular fish to be photo- 
graphed, otherwise a most unnatural effect will 
be produced. Fanciful or elaborate backgrounds 
should never be employed, as they only serve 
to distract the attention from the fish, and pro- 
duce a very artificial effect. 

Before attempting to photograph a fish, it 
should be kept under observation for some time 
in a roomy, well-oxygenated aquarium, so that 
its habits and characteristic positions may be 
studied and noted down. When first placed in 
the photographic tank, the fish will probably 
dash wildly about, sink to the bottom, and 
skulk away into the corners. It is no use at- 
tempting to begin photographic operations until 
the fish has got over the fright of being trans- 
ferred from the stock aquarium to the photo- 
gtaphic aquarium, and has become somewhat 
accustomed to the strong light illuminating the 
latter. F. M-D. 


FISH-EYE CAMERA (Fr., Chambre a4 eil de 
poisson ; Ger., Fischenauge-kamera) 

J. Alan Stewart, M.A., has published a method 
of obtaining photographs resembling the views 
that would be seen by the eye of a fish. Objects 
against the light of the sky are only perceived 
by the fish when they fall within the limits of a 


252 Fixed-focus Camera 


right-angled cone, whose apex is at the fish’s 
eye, while the base is a circle on the surface of 
the water, of a little larger radius than the 
depth of the fish. To produce a photographic 
imitation of these conditions, a box having a 
pinhole instead of a lens was employed. Although 
light-tight except to rays entering by the pin- 
hole, the box was not watertight, but admitted 
water freely. The sensitive plate was placed 
5 in. from the pinhole and the camera was 
immersed in a larger box filled with water, the 
exposure being then made on an object—a 
phantom minnow, for example—3 or 4 in. below 
the surface of the water in the exterior vessel. 
An isochromatic plate was used, satisfactory 
results being obtained with five minutes’ expo- 
sure in bright sunlight. 


R. W. Wood advises the following procedure :’ 


A small pail is taken, and into this, rather over 
half-way up, is fitted a metal disc having a 
perforated pinhole. The photographic plate is 
laid at the bottom of the pail in the dark-room, 
and the pail is filled with clean water, both 
above and below the metal disc. The pail, which 
is now practically a camerz, is stood on the 
ground and covered with a sheet of glass, which 
must touch the surface of the water, so that 
air does not come between—this preventing 
ripples. Very interesting vertical pictures may 
be made with the apparatus. To work horizon- 
tally (in the manner in which a fish would 
observe things through the sides of an aquarium), 
a watertight box is made, with an opening in 
one end. A piece of looking-glass is then taken, 
and a pinhole is made in the film of amalgam on 
the back, the glass being then cemented over the 
opening in the box with the unsilvered side out- 


ward. In the dark room, a plate is inserted, the 


box filled with water and the cover replaced. 
A little more water is added, through a small 
hole provided for the purpose, in order to dis- 
place any air that is present. Some remarkable 
results are obtained with this camera, which will 
photograph objects close to the tripod, besides 
those nearly due right and left, and directly 
ovethead. Naturally, there is a certain amount 
of distortion, especially at the margins of the view. 


FISH-GLUE (Fr., Colle de poisson ; Ger., 
Fischleim) 

The product obtained by boiling fish-skins 
and other waste remaining from fish-curing, and 
manufactured principally at Gloucester, Mass., 
U.S.A. The glue thus procured is permanently 
liquid, and in a more or less viscous form. It 
is largely used by photo-engravers for the enamel, 
enameline, or fish-glue process, but for this pur- 
pose it is clarified by boiling with albumen. The 
glue is preserved with oil of wintergreen. 


FISH-GLUE PROCESS 

This is described under the heading of “ Enam- 
eline,”’ by which name it was originally intro- 
duced as a secret process, 


FITCH-HAIR BRUSH 
A brush made from the hair of the polecat. 


FIXED-FOCUS CAMERA 
A camera in which the relative positions of 
lens and plate or film are fixed. Such cameras 


ve 


; 
J 
: 
. 
; 


Fixed White 


are usually of a cheap class, although some of 
the smaller ones are fitted with lenses of high 
quality. The advantages of a  fixed-focus 
camera are mainly simplicity and readiness for 
work at a moment’s notice. These cameras are 
frequently fitted with supplementary lenses, or 
magnifiers, which permit of near objects being 
age at fixed distances, usually 3, 6, 9 and 
12: Kt. 


FIXED WHITE (See “‘ Barium Sulphate.’’) 


FIXING 

The term “ fixing ”’ is a misnomer, as, instead 
of making permanent something that is desired, 
it removes something that is not desired, and 
which, if left in the negative or print, would 
seriously impair it. Fixing, in photography, 
means the removal of any sensitive salt unacted 
upon by light, or by the developer, thus render- 
ing the negative or print unalterable by the 
further action of light. The quantity of silver 
reduced (developed) in a negative bears a very 
small proportion to that originally in the plate 
—very small both in film depth and surface 
measurement, only the highest lights going all 
the way through the film, while in the shadows 
and darker parts little more than the surface is 
touched. Thus in the average developed film 
there remains a large proportion—estimated at 
75 per cent.—of unaffected silver bromide which 
must be removed before the negative can be 
examined with safety in daylight, or be used for 
printing. 

Several substances possess the property of 
dissolving this unreduced silver. Sodium hypo- 
’ sulphite has the greatest solvent action except 
ammonia, which for many reasons it is not 
advisable to use. Although many solvents of 
silver are known, ammonia, potassium cyanide, 
and sodium hyposulphite (better known as 
“hypo’’) are the most notable. Ammonia, 
however, is not practicable, because to remove 
the superfluous silver quickly a very strong 
solution must be used, and such a solution 
seriously damages a gelatine film. Potassium 
cyanide, though used as a fixer for wet plate and 
ferrotype work, is too expensive for modern dry 
plates and papers, and in addition is undesirable 
because of its exceedingly poisonous nature 
and its liability to eat into the half-tones. 
The colour of the negative after fixing with 


cyanide is by reflected light whiter than when — 


**hypo”’ is used, but by transmitted light, as when 
printing, it is browner and consequently more 
actinic. All things considered, however, it is 
not so good as “‘ hypo.” It was in the year 1819 
that Sir John Herschel discovered in sodium 
hyposulphite a solvent for unreduced silver, but 
the first use of it is credited to J. B. Reade, 
who in 1837 made the first fixed silver prints 
from paper negatives. “Hypo” was at that 
time a very rare salt, and expensive, costing 
about half a crown an ounce; in 1845 it dropped 
to 6d. per ounce, in 1857 to 6d. per pound, since 
when it has become very cheap indeed. 

The usual procedure in fixing negatives is to 
place them film upwards in a flat dish filled with 
the “hypo” solution, but while such a method 
serves very well, particularly when the solution 
is frequently agitated, the work is performed 


253 


Fixing 


more quickly and efficiently if the plates are held 
vertically in the solution, which should be in 
porcelain tanks (as B), or lead-lined zinc tanks. 
These tanks must be deep and formed with a ridge 
in the bottom (see B), on which the plates rest 
while the grit and other impurities settle below 
them. Plates fixed in flat dishes often appear 
correctly fixed except for small white (unfixed) 
patches caused by impurities resting on the film, 


iN! a 

TAM (i 

Py i eet) 

A mi \\ 
al WiLL 


1 
il 


A. Wooden Tank B. Porcelain Tank 
and preventing the action of the “hypo.” In 
a vertical tank a dozen plates may be fixing at 
one time, and take up but little room. When a 
flat dish is used the plate should be film side 
down, but not with the film in contact with the 
dish, and then impurities cannot easily attach 
themselves to the film; even this is not so good 
as vertical fixing. A shows a form of dish for 
fixing plates upside down; the long V-shaped 
wooden trough, covered with pitch or made 
waterproof and watertight in some other way, 
is filled with the fixing solution, and the plates 
rested on the sloping sides film side downwards. 
An advantage of such a dish is that it may be 
used for any and all sizes. Such a dish is more 
cumbersome, and takes up more room, than a 
vertical trough. 

It is not necessary to deal here with the com- 
position of ‘“‘ hypo” fixing baths, as formule 
have been given under the headings “ Acid 
Fixing Bath” and “ Alkaline Fixing Bath.” 
While fixing is apparently the simplest of all 
photographic operations, it is frequently done 
in an inefficient manner, thus leading to many 
failures. A common mistake is to remove the 
negative or print from the “ hypo ”’ solution too 
soon, A negative is not fixed the moment the 
silver appears to be dissolved away and the 
plate clear. The process of fixing with “hypo” 
includes two distinct and important functions. 
The first is the formation of a double salt of 
sodium hyposulphite and silver by the reaction 
of the creamy white silver bromide with the 
“hypo,” at which stage the negative is clear 
and apparently fixed. The double salt so formed 
is insoluble in water, and therefore cannot be 
removed by any amount of washing; it cannot 
be seen, and the negative appears perfect and 
ready for washing and drying, but if washed and 
dried at this stage the double salt will on exposure 
to light appear in due course as a yellowish stain, 
and in time the image will fade more or less to 
an extent corresponding to the amount of the 
double salt in the film. The second function 
is the dissolving away of the detrimental salt 
first formed. Although insoluble in water, a 
longer soaking in the “ hypo”’ solution converts 
it into another double salt that water will easily 
remove; hence the absolute necessity of leaving 


Fixing 


the developed plate in the fixing bath for an 
additional time after the plate appears to the eye 
to be fixed and clear. Ordinarily, the proper 
length of time to secure perfect fixation is double 
that taken by the white substance to dissolve. 
Thus, for example, if it takes ten minutes’ 
immersion in the “hypo” bath to clear away 
the last traces of the silver bromide, the plate 
must be allowed to remain for another ten 
minutes in order that fixation may be complete. 

Some workers advocate a second fixing bath 
rather than a prolonged soaking in one bath, but 
if the first bath is fresh, properly mixed, and of 
the correct strength, a second fixing bath should 
be quite unnecessary. If the fixing bath is so 
weak or so loaded with impurities that it is unable 
to perform its work, it should be discarded, as 
it is in a condition to do harm a second bath 
cannot correct. 

Where a variety of developers are in use, and 
if no care is taken to wash the plates thoroughly 
free from developer before placing them in the 
fixing bath, there is a possibility of trouble arising 
if the same bath is in use for all plates; but there 
is quite as much risk of having the transparency 
of the gelatine impaired by failure to wash off the 
developer even when a freshly made bath is 
used. 

A common mistake is to employ “hypo” 
fixing baths too strong. The silver bromide is 
less soluble in, say, a 50 per cent. solution than 
in a 25 percent. solution. The latter, 4 oz. of 
““ hypo ”’ to 16 oz. of water, is a suitable strength 
for films and plates, but for papers half or even 
a quarter strength will serve. When a very 
weak “hypo” bath is used, the double salt 
referred to is likely to remain in the film, because 
there is no excess of “hypo” to act upon it. 
The bath should not be weaker than 1 in 5 for 
plates and 1 in to for prints. A fixing bath 
made of the usual strength, the ingredients being 
properly weighed or measured and not taken 
by guesswork, and used in sufficient quantity 
to cover the plate, will contain an excess of 
““hypo’”’ that will act upon the double salt if 
time enough be given. 

A solution of “hypo” will not attack the 
actual image which has been developed so long 
as the plate is well covered with the solution, 
but when a negative wet with the fixing bath 
is exposed to the air, the “ hypo’ in solution, 
in conjunction with the oxygen of the air, does 
attack the developed (reduced) silver which 
forms the image, with the result that the nega- 
tive becomes thinner. This action is not very 
rapid, and no appreciable harm is done when 
the negative is taken out of the bath for examina- 
tion, and a reasonable time may elapse before 
it is placed in the washing water; but irrepar- 
able damage is done when the plate is left in the 
fixing bath, or in the washing water after fixing, 
only partly covered with the liquid. The 
covering of the plate with a solution of “ hypo ” 
and glycerine, and leaving it exposed to the air, 
is, in fact, a little-used method of reducing. 

As regards the exhaustion of the fixing bath, 
Messrs. A. and L. Lumiére carried out some 
experiments (published in February, 1907), and 
found that, to avoid subsequent yellowing of 
negatives on modern gelatine plates, it is advis- 
able (1) to fix not more than one hundred 


254 Fixing Before Development 


9 by 12 cm. plates in one litre of 15 per cent 
solution of “hypo” (this is roughly equal to 
about 120 quarter-plates in 35 oz.); (2) to fix 


_not more than fifty of such plates (sixty quarter- 


plates) in one litre of a 15 per cent. fixing bath, 
plus 1°5 per cent. of bisulphite; (3) to fix not 
more than seventy-five plates (ninety quarter- 
plates) in one litre of a 15 per cent. fixing bath 
plus 1-5 per cent. bisulphite and -5 per cent. 
chrome alum. The moment when the fixing 
bath is used up and should be thrown away can 
be determined by placing a drop of the bath 
on white paper, and exposing for some time to 
light and air; if the spot turns brown, the bath 
is exhausted. 

The function of the fixing solution is the same 
for prints as for negatives, although the silver 
salts may differ chemically and may be attacked 
under different conditions. The porous paper 
allows the “‘ hypo” to act on both sides of the 
film, but this is more than counterbalanced by 
the larger amount of water that must be dis- 
placed before the “hypo” can begin its work 
of dissolving the silver bromide. 

While, on the whole, a plain solution of 
“hypo ”’ is sufficient for the fixing of negatives 
and silver prints, several additions have from 
time to time been recommended, some with a 
view to hardening the film and so prevent frilling 
and blistering, others to prevent or remove stains 
from the film, and still others to keep the solu- 
tion itself from being discoloured in cases where 
it is employed over and over again. The most 
harmful, and at the same time the most frequently 
recommended, addition is common alum, which 
decomposes the “ hypo,” liberating sulphur, and 
forming injurious compounds that may possibly 
interfere with the fixing, and lead to degradation 
of the negative or print. 

As the result of a series of experiments, Messrs. 
Haddon and Grundy have stated that the hest 
strength at which to use a “‘ hypo ” bath is 10 per 
cent., and that such a bath will at a normal 
temperature completely fix a print in ten min- 
utes. As to the exact amount of “hypo” to 
be used for each print, this depends on many 
circumstances, but on an average 2 oz. of “ hypo” 
dissolved in 20 oz. of water will thoroughly fix 
420 sq. in. of print—that is, one sheet of paper 
24 in. by 17} in., equal to about thirty quarter- 
plate prints or about ten or eleven half-plate 
prints. Otherwise stated, it requires approxi- 
mately from 80 grs. to 90 grs. of “hypo” in the 
form of a Io per cent. solution to fix a half-plate 
print at normal temperature, immersing the print 
for ten minutes. ; 

In process work, wet collodion negatives are 
invariably fixed in potassium cyanide, the usual 
formula being 1 oz. of 30 per cent. cyanide in 
20 oz, of water. 


FIXING BEFORE DEVELOPMENT 


It has been found that whatever the action 
of light may be on the sensitive silver salts, the 
result is such that it is not destroyed by fixa- 
tion; and it has been suggested that when on 
tour it may be convenient or safer merely to 
fix the exposed plates and then develop them 
on thereturnhome. In such a case the developer 
is a physical one, and the most satisfactory is 
that given on the next page. ; 


‘Fixing Before Toning 
A. Ammonium § sul- 
phocyanide . 2,304gfs. 240 g 
Silver nitrate 384 «;, 40°53 
Sodium sulphite . 2,304 ,, EV Bee 
“Hypo” Je 5 480 5; 50 ,, 
Potassium bromide 657 ,, Gas 
Distilled water to 20 0Z. 1,000 ccs 
B. Metol : i  Y44 BFs. I5 g 
Sodium sulphite . 70m TEC. 
Distilled water to 60 RODe CCS: 


For use, mix 6 parts of A with 54 parts of 
water, and add 30 to 40 parts of B. As a 
practical process this is hardly worth trial, as 
the exposures must be at least four to six times 
longer than usual. 


FIXING BEFORE TONING (See ‘“ Toning 
after Fixing.’’) 


FIXING, COMBINED DEVELOPING AND 
(See “Developing and Fixing Com- 
bined.”’) 


FIXING, COMBINED TONING AND (See 
“Toning and Fixing Combined.’’) 


FIXING, DEFERRED 

A process for treating a negative after devel- 
opment so that fixing may be carried out later. 
The method is largely used by tourists who desire 
to see whether exposures have been correct, but 
who do not wish, for the time being, to go to the 
trouble of fixing and washing. The plate is 
developed as usual, washed for about five min- 
utes, and placed in any one of the three following 
baths, thus rendering the developer inert :— 


(1) Potassium bromide $ 0z., water 5 oz. 
(2) Alum $ oz., citric acid 30 grs., water 5 oz. 
(3) Cadmium bromide } 0z., alcohol 5 oz. 


In hot weather add 15 drops of formaline. Five to 
ten minutes’ treatment is sufficient. The safest 
bath is the bromide bath (No. 1); should the alum 
bath (No. 2) be used and the plate not be propertly 
washed, ugly stains may appear. With formule 
Nos. 1 and 2, a slight rinsing after the “ defer- 
ting’”’ bath is necessary, the plate being then 
dried and fixed at leisure. The advantage of the 
cadmium bath (No. 3) is that the plate need not 
be washed either before or after treatment, and 
the alcohol serves to dry the plate in a very 
few minutes. Daylight does not injure negatives 
temporarily finished in this way, and they may 
even be printed from, preferably upon bromide 
or gaslight paper. 


FIXING WITHOUT TONING 

All printing-out papers do not need toning, 
and in some cases good colours may be obtained 
by fixing only. (See ‘“‘Self-toning Papers.’’) 
Plain salted paper fixes out a pleasing sepia 
colour, if not too heavily sized. Paper prepared 
with silver chloride alone comes out of the 
fixing bath a blue colour, while if the organic salt 
is chiefly used a foxy red results. A combination 
of these two colours in right proportion results in 
a pleasing tone on fixing. Effective red tones 
may be obtained on ordinary matt P.O.P. by 
fixing without toning. Printing should be 
deeper than usual, and the prints washed well 
before fixing, in order to remove the free silver. 


255 


Flake White 


FIXING-HARDENING BATHS 

Solutions for hardening the films of plates and 
papers and at the same time fixing the image. 
Their use does not yield such permanent results 
as the use of separate fixing and hardening 
baths. (See ‘‘ Hardeners.’’) The best known 
formule are :— 


Alum “ Hypo” 
Alum (saturated sol.) 20 oz. TOO ccs 
Sodium sulphite (sat- 
urated solution) . 6 ,, S00) 5 
‘Seiypo'. sol. {-in! §).-20 -,, TOO 
Chrome Alum “ Hypo” 

Add— 

Strong sulphuric acid 60 drops of Dares 

Water . ‘ ie OZ, 50 ccs. 
to— 

Sodium sulphite sf 21m: 50 ccs. 

Water P ‘ as pe BEG 
and pour the mixture into— 

“Hypo: ‘ - 16 02. 400 ccs 

Water ; ° ey, au 1,200 4 
Finally add— 

Chrome alum . BENE) tage) > 25 ccs. 
Water ‘ ‘ ne cee 20 7. 
“Hypo” Acid Sulphite 
“Hypo ’”’ (in powder) 1 Ib. 250 g. 
Sodium acid sulphite 2 oz. 42%, 

Water p : rid « Wey tae 1,000 ccs. 


The second and third baths, being in an acid 
condition, must not be used for printing-out 
papers, and are suitable only for plates and 
bromide and gaslight papers. The “hypo” 
and plain alum bath may, however, be used 
after toning. 

Another form of fixing-hardening bath, which 
is largely used in hot countries and in England 
during hot weather, is the following :— 


Sodium hyposulphite. 2 oz. 220 g. 
Potas. metabisulphite #5, 25: % 
Chrome alum . 5 ee oh te 


' Water : 16k, 1,000 ccs. 


First dissolve the ““hypo” in 5 oz., half of the 
water made hot, next the metabisulphite in half 
the remaining water (cold), and add to the 
“hypo” mixture; lastly dissolve the chrome 
alum in the remaining water (cold), and add 
to the hypo-metabisulphite mixture. Careless 
mixing causes turbidity, whereas the solution 
should be clear and of a greenish colour. The 
above being acid is suitable for negatives and 
bromide and gaslight prints, but not for P.O.P. 


FLAKE WHITE 

Basic lead carbonate, used as a white pig- 
ment for retouching photographs, etc. 

In process work, flake white has been super- 
seded by other pigments, and is now seldom used 
for retouching photographs for reproduction 
owing to its tendency to become yellow. The 
more modern white pigments employed, such 
as albanine, ullmanine, blanc d’argent, etc., are 
described under their respective headings. 


Flap Shutter 


FLAP SHUTTER (Fr., Obturateur d volet ; Ger., 
Klappverschluss) 

A shutter in which the exposure is made by 
the rise and fall of a hinged flap. In an early 
pattern, the flap was actuated by an elastic band 
stretched from the upper part of the shutter over 


B. Double Flap 


Shutter Shutter 


a peg or projection at the bottom of the flap, 
the latter being released by depressing a catch. 
The flap fell again by its own weight. This kind 
of shutter is now seldom seen, except in studio 
apparatus. A greatly improved modern pattern, 
arranged to work noiselessly by the pressure of 
a pneumatic ball, and remaining open as long 
as the ball is pressed, is illustrated at A. The 
catch seen on the right is to keep the shutter 
raised during focusing or for time exposures, 
by engaging with a bent wire. A double flap 
shutter is shown at B. Another form of flap 
shutter is really nothing more than a hinged 
covering for the lens, lined with velvet and 
worked by means of a rod projecting outside the 
camera, With this, however, exposures suffi- 
ciently quick for studio work are readily given. 


FLARE SPOT 


A light patch usually near the centre of a 
photograph, and caused by internal reflection 
in the lens. It may usually be obviated by 
altering the position of the diaphragm, so that the 
reflected light becomes evenly distributed over 
the entire field. One form of flare takes the 
shape of a well-defined inverted image of a 
window, portion of sky, or other bright object. 
This is usually termed a “ ghost” and may be 
obviated by the method above indicated. Flare 
usually appears when using a small diaphragm ; 
hence many lenses which work satisfactorily 
down to f/16 exhibit flare when stopped down 
to a smaller aperture. (See also “ False Images.”) 


FLASH LAMP (Fr., Lampe éclaiy ; Ger., Blitz- 
lampe, Magnesitumlampe) 

In its original sense, a lamp for burning mag- 
nesium powder, which is blown through a spirit 
or gas flame. A simple type of flash lamp may 
be made as shown at A, with a short metal pipe 
bent to a right angle and surrounded with cotton- 
wool soaked in methylated spirit. A charge of 
powdered magnesium is placed in the pipe, and 
the free end is attached to a rubber tube ter- 
minating in a ball. The spirit is then lit, and 
pressure on the ball at the desired .moment 
drives the magnesium into the flame and ignites 
it. A number of such lamps may be arranged 


256 Flash Lamp 


to flash simultaneously by connecting all the 
pipes to a single large ball, a pair of bellows, a 
bicycle pump, or an air reservoir. It is always 
preferable, when extra light is desired, to use 
several lamps, rather than to increase the charge 
of powder in a single lamp; as, in the latter 


is a 
SS 


A. Simple Type of Flash Lamp 


case, much of the powder may simply be driven 
through the flame without being consumed, and 
so be wasted. Flashlight mixtures should on no 
account be used in enclosed lamps; these are 
only suitable for plain magnesium powder. A 
popular commercial flash lamp of the enclosed 
type, which gives either an instantaneous or a 
continuous flash, is shown at B. To use this, 
the metal chamber is half filled with magnesium 
powder, and about an ounce of methylated spirit 
is poured into the vessel holding the wick, taking 
care that none gets into the discharge orifice or 
over the sides of the reservoir. The rubber tube 
is then closed by means of the spring clip, and 
the bladder is inflated until it fills the net. The 
wick having been lit, a flash of the required 
duration can now be obtained by pressing the 
clip. After exposure, the flame is extinguished 
by replacing a metal cap. 

The term flash lamp is now also used for open 
arrangements in which a flashlight mixture, con- 
sisting of magnesium powder mixed with potas- 


ee 
— 


x Cline 45 


B. Enclosed Flas C. Open Flash 
Lamp Lamp 


sium chlorate, or other detonating ingredients, 
is burnt in a metal tray or pan, by means of a 
fuse which is operated from a small accumulator, 
the mechanical striking of a match ot percussion 
cap, or other means. A typical flash lamp of the 
open type is illustrated at C. The ignition of the 
powder is obtained in a somewhat novel fashion, 
A milled disc of a special pyrophorous or spark- 
giving metal is caused to rotate against a similar 


a 


7 ee we er: ey 


(SHAILVDUN AHYHL HO SLYVd WOW) ONILNIYd NOLLVNIANOD 
NOSNISOY ‘d ‘H (ALVI AHL) AG LASNNS GNV NAVG 


Flashlight Candles 


metal surface by means of a coiled spring, thus 
giving off a small stream of sparks as it revolves. 
The spring is wound up by a key and the powder 
is spread on the tray around the milled disc, 
when pressure on the pneumatic bulb at once 
starts the mechanism and ignites the flash 
mixture. For professional flashlight purposes, 
longer trays are commonly used, the powder 
being laid in a thin, heaped-up line. The lamp 
is raised to a suitable height by a jointed metal 
tod attached to a stand; and a screen or cover 
of muslin, or other light, translucent material, is 
supported on a frame over the tray to diffuse 
the illumination. 


FLASHLIGHT CANDLES 
Flashlight.’’) 


FLASHLIGHT PHOTOGRAPHY 

The taking of photographs by means of 
flashes of artificial light, the light being generally 
produced by burning magnesium or flashlight 
mixtures. Magnesium was made known in 1808 
by Sir Humphry Davy, but for half a century or 
more it was regarded as a curiosity. In 1859 
Bunsen, of Heidelberg, and H. E. Roscoe, of 
Manchester, pointed out the value of magnesium 
as a source of light for photographic exposures, 
Improvements in the manufacture of the metal 
took place (a company being formed in Man- 
chester for the purpose in 1863), but its expensive- 
ness (magnesium in the form of ribbon then cost 
half a crown per foot) kept its use restricted. 
A. Brothers, of Manchester, has been credited 
with taking the first successful photographs with 
magnesium, for early in 1864 he obtained a 
stereoscopic negative of a Derbyshire mine, and 
in May of the same year a portrait of Prof. 
Faraday, at the Royal Institution. In the 
following year the interior of the great Pyramid 
was taken by Prof. P. Smith by magnesium 
light, since when the metal, in the form of both 
ribbon and powder, has become cheaper and 
consequently widely used. The light given off 
is of intense brilliancy and of high actinic power. 

Magnesium for photographic illumination pur- 
poses may be obtained in three different forms— 
pure magnesium powder; flattened wire, known 
as ribbon ; and a combination of magnesium and 
other substances, in powder. ‘The ribbon is the 
safest, but does not allow of such short exposures 
as the powders; however, it is commonly 
employed in photographing dark corners of 
rooms, caverns, cellars, etc., where the length of 
the exposure is not of much consequence, and 
it is sometimes useful as an accessory to day- 
light, as a means of illuminating objects in deep 
shadow, since, on account of its burning slowly, 
it may be moved about while the exposure is 
being made, and so give diffused lighting. 
Another advantage of using ribbon is that the 
actinic value of the light obtained by burning a 
definite quantity remains constant under the 
same conditions, so that by measuring the length 
—or, preferably, weighing the quantity—of the 
ribbon before burning, the photographer can 
easily obtain data that will assist him in making 
the results of later exposures sure. 

For flashlight work proper—that is, for what 
are known as “instantaneous exposures ’’— 
the powders must be used. It is not necessary 

17 


(See ‘* Candles, 


257 


Flashlight Photography 


to employ a shutter as in making instantaneous 
exposures by daylight; in most cases the 
ordinary lights of an apartment are too feeble 
in actinic rays to affect the plate, and the lens 
is left open until after the flashlight. Magnesium 
flashes are open to objections: the quantity of 
smoke produced, and the difficulty of diffusing or 
spreading the light over a sufficiently wide area 


epee re 


Wy Magnesium 
Flashlight 


Reflector 


7 area 


A. Simple Arrangement for Flashlight 
Portraiture 


to obviate harsh shadows and hard contrasts. 
Again, there is the risk of explosion, but such an 
accident can scarcely occur with careful, proper 
firing. Pure magnesium powder gives a bright 
and highly actinic flash, but it must be blown 
through a flame. Flashlight powders containing 
substances in addition to magnesium are really 
explosive mixtures, and they must be ignited 
by applying a light, for should they be blown 
through a flame a dangerous explosion will 
result. A flashlight compound must not be 
used in a closed storage reservoir or magazine 
lamp, because in these the flame would travel 
to the bulk and explode it. Only the pure 
magnesium powder should be used in such lamps. 
For the beginner, the ribbon is the safest and the 
pure powder the next safe. 

As regards the amount of powder to be used, 
this depends upon nearness of subject, stop, 
plate, etc., but the table given below (compiled © 


‘by J. H. Crabtree) may be taken as a guide :— 


mar 

s8 Size of Room 

2's Weight of Magnesium 

3:5 é required 

Py 2 Length | Breadth) Height 

Feet | Feet | Feet | Feet | Grains | Oz. (approx.): 
9 1% 6 bdo) 15 2 —_ 

15 20 6 10 30 — 

20 25 bdo) Io 75 —_ 

25 30 12 Io 120 } plus 
30 35 12 Io 180 

35 40 15 10 230 4 plus " 

40 45 15 I2 300 a 

45 50 20 12 370 — 

50 60 20 12 460 Ir plus 
55 65 20 12 560 1} plus 
60 70 30 15 680 14 plus 
65 75 30 15 780 1% plus 
70 85 30 15 goo 2 plus 
75 90 40 15 1020 2% minus 
80 95 40 I5 I200 2} 

85 100 45 20 1340 3 plus 
go I20 45 20 1500 34 minus 
95 I25 50 20 1650 32 

100 130 60 20 1850 4t 


Flashlight Photography 258 


The conditions assume a lens at f/11 and a fairly 
rapid plate, the exposure being so short as to be 
regarded as instantaneous. It is also important 
to bear in mind that the quantities specified 
must be completely burned in the flame with an 
ample supply of air, and not half consumed or 
wasted. 

Lighting and Arrangement of Subject.—Success 
in group and portrait photography by flashlight 
depends chiefly upon the arrangement of the light 
and sitter. A frequent mistake is to have the 
light at too low a level; it should be at least 1 ft. 
above the level of the sitter’s head, and not on 
a level with it or lower. The higher the light 
(in reason) the more truthful will be the effect, 
and the less like the generality of flashlight 
photographs, which are distinguished by the 
glaring whites of the eyes and the harsh blacks 
and whites. In portraiture it is a good plan 
to place the flash powder on steps as at A (see 
preceding page), or if ribbon is used the operator 
may stand on the steps and wave the ribbon 
about, or the ribbon may be tied to a stick and 
waved about on high. At B is shown the plan 


@ Sitter 


a 
= 
S 
» 
> 
ce 


al Flashlamp 


@ Ist 
Flashlamp 


BandC. Plans and Arrangements for 
Flashlight Portraiture 


of a suitable arrangement for taking portraits by 
flashlight ; a reflector of white material is needed 
on the shady side of the face, or if there happens 
to be a white wall surface on that side it will 
serve the purpose. Whitewashed ceilings serve 
admirably as a top light, as they reflect down- 
wards an enormous amount of actinic light when 
the magnesium is fired. The light is placed and 
fired at a point on one side of the camera, but 
slightly nearer than the camera to the figure, 
yet not so near as to be included in the view ; 
the flash must not be reflected in the lens, or 
the plate will be fogged. By varying the posi- 
tions of camera, sitter, light, etc., any number 
of different effects can be obtained in one room. 
If there is nothing acting as a reflector on the 
shady side of the sitter, it will be necessary to 
interpose a sheet of white tissue paper or muslin 
between the flash lamp and the subject in order 
to diffuse the light and obtain softness in the 
photograph. Frequently it is the nearness of 
the light as well as its low position that gives 
a ghostly effect to flashlight portraits. The 
diffuser is useful in the majority of cases, and 
although it stops a little of the light and may 
mean a few extra grains of powder, the results 
obtained will be softer and better. In group 
work, two or more lamps may be necessary, in 
which case one lamp should be much nearer to 


Flashlight Photography 


the group than the others (see C), all the lamps 
being fired at the same moment. Professionals 
frequently employ electrical arrangements to syn- 
chronise the ignition when more than one lamp 
is in use. The near lamp serves as the main 
light, and the other as a kind of auxiliary lamp 
to assist generally and light up to a small extent 
what would be the shady side. 

In flashlight photography all the gas, electric, 
and other lights may be left burning, as they do 
not much affect the plate during the extremely 
short exposure. If the image cannot be seen on 
the ground glass sufficiently distinct for focusing, 
the sitter or sitters can hold a candle or a lighted 
match on a level with the face, and the flame can 
then be focused. The plate is then put in, the 
dark-slide shutter is drawn, and the cap taken 
from the lens or the shutter opened, the exposure 
being made by firing the powder or ribbon. Only 
that part of the exposure made during the 
burning of the magnesium need be taken into 
consideration. 

One of the great drawbacks to the use of flash- 
light is the immense amount of white smoke 
given off. All windows and doors may there- 
fore with advantage be opened; and the smoke 
of one flash must be got rid of before another 
exposure is made. The smoke is quite harmless. 
Some of the patent commercial mixtures cause 
less smoke than others, while some of the more 
expensive and complicated flash lamps have 
smoke-catching devices. A home-made smoke- 
catching device is formed by placing the flash 
lamp in a large box stood on its end with its 
open side towards the subject; after exposure 
the lamp is immediately taken ont, the box 
closed with a cloth or tightly fitting lid, and the 
whole taken to an open window or outside and 
emptied; but the arrangement prevents much 
valuable light reaching the ceiling and walls. 

Outdoor work with flashlight differs but 
slightly from the above, but more light is 
required, and there is little or no trouble with 


the smoke. More powerful (consequently more 


explosive) mixtures, of the firework type, can 
be used, as the risk of danger to human beings 
is so much less, - 

Flashlight work is not confined to portraits, 
groups or evening work generally, but is of great 
service in illuminating dark corners in interiors, 
such as crypts, workshops, underground work- 
ings, etc., in the daytime. For this purpose 
ribbon is better than powder, but care must be 
taken to keep the naked light and the smoke 
from it out of the view of the lens, with which 
object the flash lamp may be fired behind a 
pillar or something of the sort. 

Any developer will, with care, serve for deve- 
loping flashlight exposures, but as there is always 
a risk of under-exposure and harsh contrasts, 
little or no bromide should be used, and the 
developer should be diluted with water. The 
following hydroquinone-eikonogen developer has 
been widely recommended for flashlight expos- 
ures, but metol-quinol and similar developers 
can be made to give equally good results :— 


A. Hydroquinone . #$ oz. Lista 
Eikonogen . ‘2 ae oo ae 
Sodium sulphite. 24 ,, Reac, 


Hot water to .45 ,, 1,000 ccs. 


: 
| 
| 


Flashlight Powders 


Dissolve the sodium sulphite, then the eikono- 
gen, and finally the hydroquinone. 


B. Sodium carbonate 2} oz. 
Hot water . ~ 15 


55°5 &- 
» 333 CCS. 


For use take 3 oz. of A, I oz. of B, and 3 oz. 
of water; this forms a normal developer which 
should give a good negative in from eight to ten 
minutes. 


FLASHLIGHT POWDERS 

The chief two kinds of flashlight powders are 
(1) pure magnesium powder and (2) mixtures of 
magnesium and other substances. Magnesium 
powder used alone is blown through a flame, the 
brightness and duration of the flash depending 
upon the quantity of powder burnt and upon 
the length of time taken in passing it through 
the flame. Some arrangements for firing permit 
of a slow passage of the powder through the 
flame, in which case the light is continuous, and 
not an instantaneous flash; others permit of a 
large quantity of the powder being passed through 
a flame very quickly, in which case there is fre- 
quently a risk of much of the powder being 
wasted. 

Flashlight mixtures are explosive, and in their 
action behave like gunpowder; they must not 
be blown through a flame, but must be placed 
in a heap or a ridge and the light applied, the 
result being a momentary flash of high actinic 
power. Such explosive mixtures must always 
be looked upon as being more or less dangerous. 
The addition of chemicals to the magnesium is 
for the purpose of increasing the rapidity of the 
combustion and the actinic power of the light. 
When such mixtures are made by the worker, 
the ingredients should be purchased in the 
powder form and then mixed carefully together 
on paper with a dry feather. Large quantities 
should never be mixed for fear of explosions, and 
for the same reason there should be no lumps of 
any kind in the mixtures. The ordinary photo- 
gtapher will be well advised in buying his flash- 
light mixtures ready prepared. Some of the 
best known formule are :— 


(1) Magnesium , s . 6 parts 
Potassium chlorate . ek sae 
(2) Magnesium : ‘ CPR <a 
Potassium chlorate a Le Ae oe 
Potassium perchlorate - & 435i 
{3) Magnesium : : wR aig 
‘Potassium chlorate . J: i; Smt 
Antimony sulphide . rae aie 
(4) Magnesium F : ae (eee 
Potassium perchlorate nner Siew 
Potassium nitrate . sinh, via 
{5) Magnesium < .  *. rose 
Ammonium nitrate . ects Bases 
Strontium oxalate . ° Rises 
Sodium oxalate ss . Bley 
(6) Magnesium ‘ : 4b AOL X55 
Potassium perchlorate a: eee 
Sodium chloride (salt) ga iy woe 
Barium tartrate ; é eee 


Nos. 1 and 2 are good average mixtures for 
home work or professional portraiture. No. 3 
gives a very good light, but its fumes are poison- 
ous, and it should therefore be used in the open 
air or in a well-ventilated room where the fumes 


259° 


Flattening Prints 


can escape quickly. No. 4 burns rapidly, and 
is less liable to explode. No. § is for isochro- 
matic plates, and a yellow screen should be used 
in the lens. No. 6 is for isochromatic plates, but 
a yellow screen need not be used. 

Aluminium is said to give less smoke than 
magnesium, but it yields only about two-thirds 
of the actinic light. The following mixture of 
aluminium and magnesium not only gives less 
smoke than a mixture containing chlorate, but 
the smoke quickly passes away and the powder 
is non-explosive :— 


Copper sulphate (anhydrous) 6 parts 
Magnesium powder , Ar os a 
Aluminium powder ; (el batt Beee 


This gives much less smoke than mixtures con- 
taining chlorate, and the smoke passes away 
quickly, thus allowing of a series of successive 
exposures in a room. (See also “‘ Aluminium 
Flashlight.’’) 

There are many other formule for flashlight 
mixtures, but they are similar to the above. 

Great care is necessary when firing flashlight 
mixtures; and when no proper lamp is used the 
powder is best placed on a small iron slab or 
tray and fired by means of touch-paper (which 
see), or by means of a long taper or of a match 
fixed to a stick, the operator turning his head 
away when the actual flash takes place. 

Slow-burning mixtures may be made, the 
following being a typical formula :— 


Magnesium powder 100 parts 
Ceric nitrate : : a FOL 
Strontium carbonate . PON: + seNG% 


Eighty grains of this powder burn in about six 
seconds. 

Flash-sheets are made by soaking thin blotting- 
paper in a strong solution of saltpetre, drying, 
and then spreading over the paper pure dried, 
unoxidised magnesium powder, leaving the 
edges free. Such a sheet constitutes a com- 
bined slow-match and flashlight, it burning 
slowly until the smoulder reaches the powder, 
which then bursts into a bright flame. Flash- 
sheets are quite safe in use; a commercial form 
is a mixture of fine magnesium powder and cellu- 
loid spread on glass and allowed to dry. 


FLATNESS 

A term applied to a print in which there is 
but little contrast between the lights and 
shadows. It is the opposite quality to brilliance. 
An ovet-exposed and under-developed negative 
gives a flat result. 


FLATTENING PRINTS 

Prints that are not dried under pressure 
invariably curl up. Prints on collodion paper 
may be dried between blotting-paper under 
pressure, but gelatine prints—ordinary P.O.P., 
bromide and gaslight papers—cannot be treated 
in this way, because of the sticky gelatine sur- 
face. Sometimes even collodion prints will curl 
badly when removed from pressure. A rough 
and ready method of flattening is to roll the dry 
prints all together film side outwards, and 
secure with an elastic band: after a few hours 
they will be found on unrolling to be flat. A 
better method is here illustrated. The curled 


Flexible Support 


picture is laid face downwards on a clean flat 
surface, and a flat ruler is then placed along one 
edge of the print and pressed down firmly. 


S) 
Ne, 
ST] A 
SLRS 
A 


SS OL 


Flattening Prints 


Next, the whole print is drawn sharply under the 
ruler, as illustrated, the ruler being kept station- 
ary. The process may need to be repeated 
once or twice. 


FLEXIBLE SUPPORT (See ‘“ Temporary 
Support.’’) 


FLORENTINE FRAMES (Fr., Cadves floren- 
tins ; Ger., Florentinischer Rahmen) 
Ornate gilt frames with open-work foliated 
ornament; suitable for photographs worked-up 
in water-colours, crayons, etc., when not on too 
large a scale. 


FLOWERS OF SULPHUR (See “ Sulphur.”) 
FLOWERS AND FRUIT, PHOTOGRAPHY 
OF 


In this work success depends on the lighting, 
the arrangement of the subject, and the method 
of exposure. Flowers and fruit may be photo- 
graphed indoors or out, in their natural sur- 
roundings or otherwise; but the best results 
are obtained by arranging them indoors and in 
a suitable light. A convenient method of 
arranging the lighting is shown at 
A and B. On a table near a window 
on the shady side of the house the 
flowers (or fruit) are arranged, the 
background being a sheet of brown or 
other coloured paper, according to the 
tint required in the photograph. It 
is advisable to have papers of several 
different colours at hand, and to bear 
in mind their different photographic 
values. The light should come in at 
the window and be fairly strong, as 
then, by means of tissue paper over 
the lower half of the window and a 
white cardboard reflector on the 
shady side of the subject, the light 
may be controlled to a nicety. The 
positions of the camera, flowers, back- 
ground, etc., are all subject to experiment 
in obtaining various effects. It is not always 
advisable to show the vase which contains 
the flowers or the means of supporting the 
fruit. In the case of a few blooms, they may 
be stood in a narrow-necked bottle in order to 
keep them upright, and the stalks must be 
long if the neck of the bottle is not to be 
included in the picture. Other supports include 
a bowl of wet sand; bent strips of sheet lead; 
and a large potato, the stalks in all these cases 
being long. For the purpose of picturing the 


260 Flowers, etc., Photography of 


vase as well as the flowers or fruit lying upon 
the table, there should be no dividing line 
between table and background, for which pur- 
pose the paper forming the background should 
be brought in a gentle curve underneath the 
vase, etc. Even if a line would enhance the 
pictorial value of the picture, it should not be 
abrupt. The table-cloth must not be of a pro- 
nounced pattern, or of a colour contrasting too 
strongly with the background. 

Cameras are sometimes used vertically for 
photographing flowers that are lying, for example, 
on the floor. Similar results may generally be 
obtained with an ordinary camera used in the 
usual way, by arranging the vertical back- 
ground to take the fruit or floral sprays; this 
may be done by using stout, stiff cardboard 
covered with coloured paper as the background 
and pushing pins through from the back, their 
points serving as rests and being covered by 
the objects photographed, although if they are 
not hidden they will be scarcely noticeable. 

Cut flowers may be preserved for photographic 
purposes by sprinkling them with fresh water, 
and while wet placing in a vase containing the 
following solution: Water 4 oz., curd soap 
2 drms., common salt 8 grs. The soap is cut 
into shreds and dissolved in the water, adding 
a small pinch of borax and the salt. If the 
flowers are to be kept for several days their 
stalks should be rinsed under the tap daily for 
a minute or so, the petals sprinkled, and the 
flowers put back into the vase. . 

The lens stop plays an important part in 
the pictorial rendering of flowers. f/16 gives 
general sharpness, but a smaller one may 
in some cases be necessary. Exposure should 
not be unduly prolonged, as some flowers— 
poppies, for example—are apt to droop during 
a long exposure and show signs of movement 
upon the plate. Isochromatic plates are the 


Pp PW8 PS 2 66 6+ oe tee eee es eceame 


' 
‘ 
9 
e 


Bachoroang 


Ground 


Window 


Flowers 


& 
S 
~ 
cS 
D 
s 
ce 


i 


eeweres 


A 
A and B. Arrangement for Flower Photography 


best for most flowers, but ordinary plates 
may be used for some with good results, every- 
thing depending upon the colour of the flowers. 
For reds, blues, yellows, and various shades 
of green an isochromatic plate is indispensable 
to give the proper values of the colours. Much 
may be done on ordinary plates by giving a 
suitable exposure—that is, one sufficiently long 
to enable the colours of little actinic value to 
register themselves on the plate. E. Seymour 
has used a yellow screen and isochromatic plate 
for only about ro per cent. of his exposures, as in 


B, 
4 
4 


Fluid Lens 261 


his opinion the use of a screen robs the picture of 
half-tone and gives an effect unsatisfactory to the 
observer of nature. Opinions differ, however, 
but there can be no doubt that to give the 
plate a full exposure for the deepest shadows and 
to develop until the highest light is of the correct 
density, is a thoroughly reliable method of 
working. In ordinary photography the goal of 
development is detail in the shadows, but if 
this is applied in flower photography, the high 
lights may become blocked up and too dense. 
Detail in the highest lights is the secret of success- 
ful flower and fruit studies; there will always be 
detail in the shadows if the exposure has been 
sufficient. The plate should on no account be 
ovet-developed, and the following pyro-soda 
developer is specially recommended :— 


A. Potassium metabi- 


sulphite I5 grs I's g 

Pyro . . 130 5, 13 5, 
Wetter, a - 20 02 1,000 ccs 

B. Sodium sulphite 2$ 0z Troyig; 
Sodium carbonate a 100 ,, 
Water . ; Tie? are 1,000 ccs 


For normal exposures take 3 parts of A and 
I part of B. For under-exposure, add more 
of B and dilute with water. 


FLUID LENS 

A glass shell, which may or may not have 
optical qualities in itself, filled with liquid. 
This arrangement is of considerable antiquity, 
and has from time to time had photographic uses. 
A fluid condenser made by Daguerre is still in 


Section of Fluid Lens 


existence; while Scott Archer, Thomas Sutton, 
and later Dr. Griin, all constructed lenses in 
which liquids played an important part. With 
the Sutton lens (see illustration) an extremely 
wide angle was obtained, but in the Archer and 
Griin lenses the special object was to gain 
“rapidity.” In the ‘illustration, a indicates 
glass, B water, and c the diaphragm. The Grin 
lens was said to contain cedar oil. | 


FLUID MEASURE (See ‘“‘ Weights and Meas- 
ures.’’) 


FLUORESCEIN (See “ Eosine.’’) 


FLUORESCENCE 

Certain substances have the power of altering 
the wave-lengths of the light or electric rays which 
fall upon them. Such bodies, when illuminated 
by ultra-violet light, become visible in darkness 
to the naked eye by emitting yellow, green, blue 


Fluorotype 


or blue-violet rays, commonly termed fluores- 
cence. Quinine sulphate, calcium tungstate, 
and barium platino-cyanide are typical fluoresc- 
ing substances. Many aniline dyes, particularly 
fluorescein, have considerable fluorescing pro- 
perties, eosine, for instance, giving a green 
fluorescence. In most cases the colour of the 
fluorescence given by dyes is complementary to 
the colour of the dye itself. 


FLUORESCENT SCREENS 


These are largely used in radiography. They 
are made by coating a suitable fabric with 
barium platino-cyanide, calcium tungstate, or 
other substances which fluoresce when exposed 
to X-rays. These screens, when used in a dark 
chamber, permit of the visual examination of 
objects placed between the X-ray tube and the 
fluorescing screen, the form and, to a limited 
extent, the structure of objects appearing as 
shadows on the screen. Of late years fluorescing 
screens have been popular for shortening the 
exposure in X-ray photography ; they are placed 
in contact with the sensitive film of the dry plate, 
and the fluorescence in conjunction with the 
direct action of the X-rays on the plate materially 
shortens the exposure. Fluorescent screens 
made of quinine sulphate are used to detect the 
presence of ultra violet light. 


FLUORESCENT TUBES 

Vacuum tubes, for use with electric currents, 
which contain traces of gases after almost com- 
plete exhaustion. When a high potential current 
is passed through such a tube it glows with 
various colours, each gas giving off a distinctive 
fluorescence. Fluorescent tubes are much used 
in spectroscopic analysis to determine the nature 
of gases. These spectra consist of bright lines 
only. X-ray tubes fluoresce owing to the small 
quantity of residual air they contain after 
exhaustion. 


FLUORHYDRIC ACID (See “ Hydrofluoric 
Acid.’’) 
FLUORIC ACID 
Another name for hydrofluoric acid (which see). 


FLUORIDE (See “ Potassium Fluoride,” etc.) 


FLUOROTYPE 

An obsolete process (invented by Robert Hunt 
in 1844) for obtaining pictures upon paper in 
the camera, so called from the introduction of 
the salts of fluoric acid. The solutions were:— 


A. Potassium bromide 20 grs. 20 g 
Distilled water I OZ. 500 ccs 

B. Sodium fluoride 5 gts. 5 g. 
Distilled water I OZ. 500 ccs 


These were then mixed together, spread 
on plain paper, and dried; the prepared paper 
was next treated with 60 grs. of silver nitrate 
dissolved in 1 oz. of water. The paper was given 
about half an hour’s exposure in the camera, 
then soaked in water, a weak solution of iron 
protosulphate brushed over it, washed in water 
acidulated with hydrochloric acid, and fixed in 
either plain water or a weak solution of sodium 
hyposulphite ; finally it was washed well. 


Fluosilicic Acid 


FLUOSILICIC ACID 
More correctly known as ‘“ Hydrofluosilicic 
Acid”? (which see). 


FOCAL APERTURE 

The effective aperture of a lens expressed as 
a fraction of its focal length. When the object 
is at a considerable distance from the lens this 
is a fixed quantity for each stop, but when copy- 
ing, the focal aperture becomes less in propor- 
tion to the size of the image. Thus a lens working 
with its largest opening at /8 on a distant object 
has its intensity reduced to f/16 when copying 
to equal size, and to f/32 when enlarging to three 
diameters. The relative exposure necessary with 
any given lens working at varying camera 
extensions may be obtained by increasing the 
exposure required for a particular aperture at 
the normal focus in the proportion of the squares 
of the normal and temporary focal -lengths 
respectively. Thus, if a lens having a normal 
focal length of 6 in. is used with a camera exten- 
sion of 9 in., the exposure with any stop will 
be increased in the proportion of 81 to 36; in 
other words, 2} times the normal exposure will 
be required. 


FOCAL LENGTH (Fr., Longueur du foyer; 
Ger., Brennweite) 


The distance between the centre of a lens and 
the screen or plate upon which the image of a 
distant object is sharply depicted. This defini- 
tion, however, is only correct in the case of a 
very thin lens, in which the thickness of the 
glass does not come into consideration, and 
in which there is only one element. In the case 
of modern photographic lenses, “ focal length ”’ 
is often taken to mean “equivalent” focal 
length ; that is to say, when a lens will render 
the image of a distant object on exactly the 
same scale as would a very thin spectacle lens, 
the two are said to be of the same equivalent 
focal length. Equivalent focal lengths vary in 
direct eae, to the size of the image 
obtained; thus, assuming that a 6-in. lens 
gives a 3-in. image of a distant object, an 18-in, 
lens will give a 9-in. image of the same object. 
This fact enables the measurement of the focal 
length of any lens to be effected by simple com- 
parison of its image with a similar image made 
by a lens of known focal length, or, better still, 
with a pinhole image. A practical method is to 
substitute for the lens a fairly small pinhole, the 
camera being extended to a convenient length 
(a length of 10 in. simplifies the slight calculation 
necessary), and to take a negative of some distant 
object having two easily recognisable points, such 
as chimneys or telegraph poles, these being 
shown a few inches apart. The distance between 
these two points is carefully measured and 
becomes a constant factor in determining the 
focal length of any other lens which can be 
focused upon the same object. Assume that the 
distance between the points is 4:5 in. Taking a 
lens of unknown focal length, it may be found, 
for example, that the images of the two selected 
points are 3 in. apart; then as 4°5 is to 3 sois 
10 to #% 3X 10 + 45 = 6-66 in. An approxi- 
mately correct result may be obtained by focus- 
ing a near object so that it appears in natural 
size upon the screen; then one-fourth of the 


262 


Focal Plane Shutter 


distance between the object and the focusing 
screen is the focal length of the lens. 

The focal length of negative lenses may be 
ascertained by neutralising them by placing 
positive lenses in contact with them until one 
is found that practically loses its convergent 
powers; then the concave lens is said to have 
a negative focal length equal to that of the 
positive lens which it neutralises. Dallmeyer’s 
method is to place a diaphragm, containing two 
small openings, in contact with the negative lens, 
which is then turned to the sun; the light pass- 
ing through these two small openings is received 
upon a white card, which is moved away from 
the lens until the two spots of light are double 
the distance apart as compared with the open- 
ings in the diaphragm ; then the distance between 
the diaphragm and the card is the negative focal 
length 


FOCAL PLANE SHUTTER 

A shutter that works immediately in front 
of the plate, and now commonly fitted to the 
highest class cameras. It is believed to owe 
its practical form to B. J. Edwards, who in 188: 
published a description of his apparatus; but 
some eighteen or twenty years previously the 
principles were known to William England, who 
used a crude device working on the same principle 
a long time before Edwards’s ideas were published. 
England’s device was a board containing a 
horizontal slit which travelled in front of the 
plate in the same manner as the drop shutter of 
the present day travels in front of the lens, 
and it was caught in a kind of bag suspended 
from the camera. A shutter of a similar nature 
had previously been experimented with by Dr. 
Mann, who recognised its power to utilise the 
whole of the light admitted by the lens. From 
1882, in which year Edwards lectured upon his 
invention before the old South London Photo- 
graphic Society, until 1892, the focal plane 
shutter seems to have been lost sight of, but 
in the latter year the Thornton-Pickard Company 
placed upon the market their now well-known 
shutter of this type, and, simultaneously, 
Stolze and Ottomar Anschutz, quite unknown 
to each other, were both working to the same 
end—the simplification and perfection of the 
shutter, more particularly, perhaps, in the 
means of adjusting the slit. 

The principle of the shutter is as follows :— 
A roller blind, containing a slit or aperture the 
whole length of the plate, is made to travel 
immediately in front of the sensitive surface. 
Assuming that this gives an exposure of 51th of 
a second, by reducing the slit to one-fifth of its 
original width the exposure is reduced to ;3,th 
of a second; again, by increasing the tension of 
the spring by five or ten times an exposure of 
sooth or yysth of a second respectively is 
obtainable. Most subjects come within the 
range of s};th to ;4,;th of a second. The 
efficiency of the focal plane shutter is greater 
than that of the lens shutter ; some types of lens 
shutter pass for only a very small proportion of 
the total exposure the whole of the light that 
the lens is capable of transmitting, much of the 
time of exposure being taken up by the shutter 
in uncovering and then covering the lens, there 
being only a brief period when the lens is quite 


Foci 


uncovered. With the focal plane shutter the 
whole of the light admitted by the lens is avail- 
able for action upon any particular portion of 
the plate uncovered by the slit; and another 
advantage is the high speed at which the shutter 
can work, rendering it indispensable for ‘“‘ in- 
stantaneous ”’ work of any kind. 

It is sometimes affirmed that the focal plane 
shutter gives distorted results, but its advocates 
affirm that the distortion (if any) is practically 
negligible. In practice, distortion may be 
divided into two classes: (a) that in which the 
outline of any one body is rendered untruth- 
fully, and (b) that in which the relative position 
of a group of figures or objects is incorrectly 
delineated ; this latter may, of course, include 
the former, and of the two is the more serious. 
While it matters but little if an image of, say, 
a rapidly moving railway train is slightly longer 
or shorter than would be the case were the train 
photographed at rest, it is a serious matter if 
the result of a closely contested cycle race is 
rendered incorrectly. To minimise any possible 
etror, the following points on the correct use of 
the shutter should be remembered. If the image 
(on the focusing screen) of the subject being 
photographed is rapidly moving in the same 
direction as the slit in the shutter, the slit must 
be made to move at a much greater speed than 
if the image and slit were travelling in opposite 
directions. The use of a shutter travelling at 
great speed in an opposite direction to that of 
the image has a tendency to shorten the object, 
while, on the other hand, the use of a shutter 
travelling in the same direction as the image 
may lengthen it. But such distortion is so 
trifling that it would be practically impossible 
to discover it. When engaged in high-speed 
work a good distance at which to work is about 
seven or eight yards from the subject. Using a 
6-in, lens at a distance of eight yards, for 
objects moving at right angles to the cameta 
these exposures would be about correct :— 


Trains, horses galloping, cycle rac- 


ing, etc. 4 ; : aposy sec. 
Men racing, jumping, etc. sty sec. 
Diving . . : : ats sec. 


If the object is taken end on—that is, coming 
towards, or receding from the camera—exposures 
three times as long as the foregoing may be 
given. By doubling the distance from the 
object, the length of exposure may be doubled. 

To develop plates which have received a 
minimum of exposure, a very energetic developer 
must be employed. The following formula is 
recommended, using equal parts of A and B:— 


A. Pyrogallic acid . 40 gts. 4°4 g. 
Metol . : ao as 3:8 ,, 
Potassium meta- 

bisulphite OL 5, Id ,, 
Potassium bromide 15 _ ,, 16 ,, 
Water to 2 20 02, 1,000 ccs 

B. Sodium carbonate. 3 oz. 164 g 

Water to. es 9 Vip ee 1,000 ccs, 


FOCI 
The plural of focus (which see). 


FOCI, CONJUGATE (See “‘ Conjugate Foci.’’) 


263 


Focus 


FOCI, VARIABLE (See “ Telephoto Lens,’’) 


FOCIMETER (Fr., Focimétre; Ger., Fokus- 
messey, Brennwettemesser) 

An instrument invented by Antoine J. F. 
Claudet, and used to test whether the chemical 
and visual foci of a lens coincide, that is, whether 
the lens is achromatic. It consists of a series 
of cards with different letters or numbers 
atranged radially on a horizontal rod, one behind 
the other, as illustrated. The middle card is 
focused sharply with the full aperture of the 


Claudet’s Focimeter 


lens to be tested, a plate being then exposed and 
developed. If the card focused is perfectly sharp 
in the resulting negative the lens is properly 
achromatic; but if one of the other cards is 
sharper, the chemical focus of the lens does not 
agree with the visual focus. By focusing the 
card that is rendered sharply in the negative 
and noticing the extent to which the screen has 
to be moved from its former position, the 
difference between the two foci and the exact 
degree of correction required will be ascertained. 
Several modifications of this apparatus have 
been suggested. 


FOCISCOPE 

A focusing eyepiece introduced by Penrose, 
the lens consisting of three elements cemented 
together, forming a very powerful magnifier of 
fairly flat field. It is useful for examining half- 
tone dot images. 


FOCOMETER (Fr., Focométre; Ger., Fokomesser) 

A lens-testing apparatus designed by Thomas 
R. Dallmeyer, for ascertaining the focal length 
of a lens, and the degree to which the various 
aberrations are corrected, or otherwise. It is 
essentially a type of optical bench. 


FOCOPLANE 
Focal plane; see ‘‘ Focal Plane Shutter.” 


FOCUS (Fr., Foyer; Ger., Brennpunkt) 

Plural, foci. The point at which the rays of 
light emitted by any luminous body converge 
after passing through a lens to form the image 
of such a body. ‘The position of the focus is 
simply demonstrated by using the lens as a 
burning glass. The focus of a lens is a position 
and not a distance, although the word is often 
so misused (see ‘‘ Focal Length’”’). The focus for 
distant objects is often called the principal or 
solar focus. 


Focus Adjuster 


FOCUS ADJUSTER (Fr., Ajusteur de foyer ; 
Ger., Fokusordner) 

An arrangement for lengthening or shortening 
the focal length of a lens, by the use of a single 
supplementary lens, or a series of such lenses of 
varying foci. A device described by John 
Traill Taylor consisted of a movable brass sliding 
piece, for which an opening was provided in the 
lens mount between the combinations. In the 
sliding piece were four apertures, each fitted with 
a thin achromatic negative lens. The appliance 
was designed for use with a doublet composed 
of two slightly meniscus lenses, which by them- 
selves did not give a flat field. With the focus 
adjuster, the focal length of the objective was 
increased to 7, 9, 12, or 15 inches, according to 
which of the four concave lenses was used, the 
field at the same time being flattened and the 
marginal pencils corrected at a fairly large 
aperture. 


FOCUS, DEPTH OF (See “ Depth of Defini- 
tion, etc.’’) 


FOCUS, EQUIVALENT (See “ Focal Length.’’) 
FOCUS TUBE (See “ Crookes’ Tube.”’) 


FOCUSER (See “ Focusing Magnifier.’’) 


FOCUSING (Fr., Mise au foyer, Mise au point; 
Ger., Einstellung) 

The action of adjusting the extension of the 
camera until the image is sufficiently sharply 
defined on the ground-glass focusing screen. A 
focusing magnifier assists in determining when 
the image is sharp by allowing slight differences 
in crispness to be more easily seen. As all the 
planes of a subject cannot be equally well 
defined, it is important to recognise which 
should show the most critical definition. Objects 
near the eye should naturally show greater 
Sharpness than those farther away. But, in 
addition, the principal object in a picture should 
show the best definition, should any differences 
exist. Where there is a number of objects at 
different distances, and it is desired to secure 
a uniform degree of sharpness between the near- 
est and the farthest, it is advisable to focus on 
a point beyond the nearest object, about one- 
fourth of the distance from the nearest to the 
farthest. 

In process work, several schemes have been 
proposed for automatic focusing. Some elabor- 
ate mechanical inventions have been devised for 
moving the camera to and from the copyboard 
at the same time as the focusing screw is turned 
to move the ground glass of the camera, but none 
of these arrangements has come into practical 
use. A more convenient method, which can be 
applied to any camera and stand with little 
alteration of existing arrangements, is the 
Scalometer system, invented by L. Emmett. 
The scalometer is an instrument made in box- 
wood, opening like a two-foot rule, there being 
on the two limbs similar scales of equal divisions 
numbered from the ends of the limbs. A cross 
tule divided into inches or centimetres bridges 
the angle formed by the opening of the two 
limbs. In operation the points or ends of the 
limbs are applied compass-like to the sides of 


264 


Focusing Glass 


the original, and then clamped at this separation. 
The cross rule is then made to slide up and down 
until it indicates across the angle formed by the 
limbs the measure of the desired reduction. At 
this point the proportional number on the two 
limbs is read off, and is marked on the back of 
the original. Then all originals which bear the 
same proportioual number can be photographed 


Scalometer for Facilitating Focusing 


together. By means of a printed scale supplied 
with the instrument it is possible to mark 
off the copying stand with numbers correspond- 
ing to those on the limbs of the instrument, 
so that the camera can be instantly set to the 
proportion number marked on the original, 
without the necessity of focusing. 


FOCUSING CAMERA (Fr., Chambre a foyer 
véglable ; Ger., Einstellungs-kamera) 

Any camera in which different distances can 
be focused for, as distinguished from fixed- 
focus cameras, which do not permit of adjust- 
ment. Self-focusing cameras are those which 
extend automatically to the correct focus for 
any given distance, on setting a pointer or 
turning a key on a marked dial. Such adjust- 
ments ate usually only to be found on hand 
cameras. 


FOCUSING CLOTH (Fr., Voile, Voile noir, Voile 
de chambre, Votle de mise au point ; Ger., 
Einstellungstuch, Kopftuch, Schwarze Lein- 
wand) 

Synonym, black cloth. A cloth used to cover 
the back of the camera and the operator’s head 
when focusing, in order to exclude extraneous 
light, which would interfere with the visibility of 
the image on the ground-glass screen. It is 
also employed to shield the top of the dark-slide 
when withdrawing the shutter, and not infre- 
quently to wrap up the slides after the exposures 
have been made. It is usually made of black 
velvet or twill, which may or may not be lined 
with yellow or red cloth, or of waterproof cloth. 
A cloth is more convenient in use when provided 
with cords at the corners for tying to the camera 
in windy weather; whilst a loop in the middle of 
one side, to slip over the lens, is always useful. 
For a small camera, the focusing cloth may be 
about 3 ft. square. . 


FOCUSING GLASS 

A name for the focusing magnifier (which see). 
The term is applied occasionally to the focusing 
screen of the camera. 


Focusing Jacket, or Rack Mount 265 


FOCUSING JACKET, OR RACK MOUNT 
(Fr., Tube a crémaillére ; Ger., Zahnstange 
Objektivrohr) 

A form of lens mount provided with an inner 
tube carrying the glasses, which slides to or fro 
“by an attached rack and pinion. This kind of 
mount is found on lantern, enlarging, and 
kinematograph objectives, and some portrait 
lenses. For lantern and kinematograph use, 
the jacket is sometimes supplied empty, to allow 
of the insertion of different objectives in loose 
interchangeable tubes or cylinders. 


FOCUSING MAGNIFIER (Fr., Loupe, Loupe de 
mise au point; Ger., Einstelloupe) 

Synonyms, focuser, compound focuser, focus- 
ing eyepiece, focusing glass. A lens used when 
more accurate focusing is desired than is obtain- 
able on the ordinary ground-glass screen, as may 
be necessary in photo-micrography, process 
work, etc. It is usually composed of two plano- 
convex lenses of identical focal length, mounted 
with their plane sides outward at a distance 
apart equal to two-thirds of the focal length. The 


Focusing Magnifiers 


lenses should preferably be achromatic, though 
this is not indispensable. To use the magnifier, 
a piece of plain plate glass having a few fine 
black lines ruled on it is substituted for the 
ground-glass focusing screen; or, as an alterna- 
tive, several microscopic cover glasses may be 
cemented at suitable spots on the ground glass 
by means of Canada balsam, having first made 
a pencilled cross on the ground surface where 
each glass is to be attached. The magnifier is 
adjusted by sliding or rotating the upper tube, 
till the ruled lines or pencilled cross, as the case 
may be, are in sharp focus, when it only remains 
to see that the image on the screen is in focus 
at the same times as the lines or cross. The 
magnifier gives an enlarged image, and naturally 
a brighter one than can be obtained on ground 
glass. A shows a magnifier with screw adjust- 
ment and clamping collar; B shows one with 
an Archimedean screw movement; C has an 
erecting lens to show the image the right way 
up; while D is provided with a bayonet tripod 
by which the magnifier may also be raised to 
examine prints, half-tone blocks, etc., if required. 


FOCUSING NEGATIVE LENS (See “ Nega- 
tive Lens.’’) 


FOCUSING SCALE (Fr., Echelle de mise au 
point ; Ger., Einstellskala) 

A graduated scale or dial fitted on hand 
cameras, enabling objects at various distances 
to be focused, by the movement of a pointer, 
without inspecting the screen. 


Focusing Uncorrected Lens 


FOCUSING SCREEN (Fr., Verre doucit, Glace 
doucie; Ger., Vistrscheibe, Mattscheibe, 
Matiglas, Mattglasschevbe) 


The screen upon which the image formed by 
the camera lens is focused, before exposing the 
plate, in order to secure sharp definition. It is 
usually of glass ground on one side to a matt 
surface. Some of the ground-glass screens 
supplied with the cheaper cameras are extremely 
coarse. A finely ground glass is, however, on 
the market in the usual cut sizes at very reason- 
able prices. A good substitute, having the 
advantage of being light and unbreakable, is a 
sheet of matt celluloid; but care must be taken 
that this does not buckle, or it will not agree in 
register with the dark-slide. For this reason 
celluloid is scarcely suitable for large cameras. 

Temporary makeshifts, to replace a broken 
focusing screen, are: white tissue paper or 
tracing paper stretched taut, a fine cambric 
handkerchief, or plain glass dabbed lightly with 
putty. For Lohse’s method of forming a focus- 
ing screen the following is necessary :-— 


Gelatine : 45 gts. 450 g. 
Barium chloride ro 150°. 
Ammonium sulphate. 73 ,, rote 
Water to. z ; 34 OZ. 1,000 ccs, 


The gelatine, sulphate and three-fourths of 
the water are heated together until dissolved ; 
the barium, dissolved in the remaining fourth 
of the water, is then added. After mixing and 
cooling, the mass is pressed through muslin so 
as to form threads, then washed and melted 
again. Finally a trace of salicylic acid in alcohol 
is added, the whole is filtered, and is then ready 
for coating upon plain glass. The solution is 
slightly troublesome to prepare, but such a 
screen may with care last a lifetime. A less 
troublesome method, due to P. R. Salmon, is 
to apply to plain glass a varnish consisting of— 


White lac . : »~ JO grs. 80 g. 
Picked gum sandarac. I2 ,, I4 4, 
Alcohol . : UR OZi- 3,000 Cee: 


C. Welborne Piper has suggested still another 
method; a dry plate should be fogged uniformly 
all over by immersion in a developer for a long 
time, fixed, bleached in a solution of 5 grs. of 
iodine and 10 grs. of potassium iodide in 1 oz. 
of water, treated with very dilute ammonia, 
washed, dried, and varnished. A screen pre- 
pared in this way, or in any of the other ways 
above mentioned, is far superior to ground glass. 

In process work, the ground-glass screen used 
has a transparent centre formed by cementing 
a thin microscopic cover glass to it with Canada 
balsam. Extremely fine focusing can then be 
done by means of an eyepiece. A cross should 
be made on the ground glass with a blacklead 
pencil before cementing down the glass, so that 
the focus of the eyepiece may be adjusted to it. 


FOCUSING UNCORRECTED LENS 

When using an uncorrected lens, that is, one 
in which the visual and actinic foci are not 
coincident, an allowance has to be made after 
focusing so as to bring the sensitive plate into 
the plane of actinic focus, The amount of this 
varies with the refractive index of the glass, but 
as such lenses are commonly made of crown 


Fog 266 


glass, it is usually safe to place the plate 4, to 
vo Of the focal length nearer to the lens. The 
correction may also be made, as in the case of 
Steinheil’s original periscope, by focusing at full 
aperture and then stopping down to t/44, or 
smaller, Another method is to place a very 
weak lens in front of the working lens while 
focusing and removing it before exposure, This 
corrector must temporarily shorten the focal 
length to the necessary degree, 


FOG (Fr., Voile; Ger., Schleter) 

A general reduction of the silver salt by the 
developer, particularly on those places which 
Should be clear glass in the negative or white 
paper in the print. The various kinds of fog 
are discussed in later articles, 


FOG, AERIAL (Fr., Voile aérien; Ger., 
Aetherisch Schleier) 

Mist, or fog, particularly noticeable in the 
distance in landscapes, due to the reflection of 
the ultra-violet and blue rays by minute par- 
ticles of water, vapour and dust. It is a factor 
to be recognised, particularly in telephotography 
and mountain work, and in such cases the use 
of colour-sensitive plates and a yellow screen, 
which cuts out the ultra-violet’ and blue, is 
advantageous. On the other hand, the peculiar 
softening effect of aerial fog is extremely pleasing 
from an esthetic point of view, and care should 
be exercised therefore not to eliminate its effects 
unduly, 


FOG, CHEMICAL (Fr., Voile chimique ; Ger., 
Chemtscher Schleier) 

A reduction of silver all over the surface of 
the plate or paper, which may be due either to 
chemical fog inherent in the emulsion, to too 
strong a developer, or to the access of actinic 
light or the use of an unsafe dark-room light. 
Fog inherent in the emulsion cannot be cured, 
but its ill effects may be somewhat obviated 
by exposing fully and adding potassium bromide 
to the developer. A clean working plate should 
stand three minutes’ development in the dark, 
without previous exposure to light, in a normal 
pyro-soda developer, and then present but the 
slightest trace of deposit. Chemical fog, caused 
by using too strong a developer, may be obviated 
by weakening the developer and by the addition 
of a little bromide. 


FOG, COLOUR, DICHROIC, GREEN, AND 
RED (Fr., Voile rouge ; Ger., Rotschleier) 

A peculiar form of fog, which is green by 
reflected light and red by transmitted light. It 
is in all cases due to silver deposited in a colloidal 
state, and shows itself most prominently in the 
shadows of a negative. It may be due to the 
emulsion itself, to traces of “hypo” in the 
developer, excess of a solvent of the silver 
haloid, such as sulphite, etc., or it may arise 
through partial fixation and reduction of the 
soluble silver salts by traces of the developer. 
This last form is often to be met with in films 
when one lies over another in the fixing bath. 
Dichroic fog is in almost all cases sensitive to 
light, and though this is not teadily noticed, it 
can be proved at once by covering up part of 
the negative showing this defect, and exposing 


Fogged Negatives 


to sunlight. It is extremely difficult to remove, 
but treatment with the following is the most 
efficacious remedy :— 


Sodium sulphite . I Oz. 50 g. 
Potassium cyanide. 100 grs. io. 
Distilled water to . 20 oz, 1,000 ccs. 


Abney has suggested bleaching the negative 
in a mixture of ferric chloride and potassium 
bromide, well washing, and then redeveloping 
with ferrous oxalate, which reduces the dichroic 
to a general fog. 


FOGGED DRY PLATES, RESTORING 

Plates which have been accidentally exposed 
to light (lightstruck is a term sometimes used), 
may be made almost as good as new, with the 
exception that their speed is reduced, by treat- 
ment for about five minutes in either of the 
following restoring baths :— 


Chromic acid ., - I5 grs. 6°25 g. 
Potassium bromide , 30° 4s i215 
Water to. ‘ «Bog. 1,000 ccs, 
Potassium bichromate 20 grs. o'9 0g. 
Hydrochloric acid . 1 drm. 25 ccs, 
Water to. : » Se 1,000 ,, 


Afterwards, the plates are thoroughly washed 
and dried. All the operations must be carried 
out in the dark-room. Plates that have been 
exposed in the camera, but have not been deve- 
loped, may be restored in the same way, but the 
immersion must be of longer duration. Plates 
restored in this way need from five to ten times 
the normal exposure. Several other methods 
are possible, one of which is to soak the plate in 
a 2 per cent. solution of ammonium persulphate ; 
Condy’s fluid (as bought), with the addition of a 
few grains of potassium bromide, also answers. 
Abney has recommended a bichromate bromide 
mixture made by dissolving 10 grs. of potassium 
bichromate in 1 oz. of water, 10 grs. of potassium 
bromide in another ounce of water, and adding 
the two together, 

Fogged dry plates can be made specially suit- 
able for transparency work by soaking for about 
ten minutes in— 


Potassium bromide . 120 grs, 12° ¢. 

Potassium iodide ant Stark se 

Hot water : $ oz. 25 ccs, 
When dissolved add— 

Hydrochloric acid . Oz. 25 ccs, 

Potassium bichromate 120 rs, 12 g. 

Water to. . + 20 OZ. 1,000 ccs. 
Wash and dry. 


The plates are made very slow by any of the 
processes named, and thus they give greater 
contrasts; hence their suitability for copying 
black-and-white work, They should also be 
developed with a clean-working developer, such 
as adurol or hydroquinone. 


FOGGED NEGATIVES, TREATMENT OF 


The method of treating fogged negatives must 


depend on the cause or nature of the fog. Deve- 
lopment fog, and fogging or staining caused by 
the plates being stale, are most successfully 
treated by thiocarbamide. A stock solution 


ee a ee ee eS ee 


Fogged Prints, Treatment of 


may be prepared, as it will keep well. The 


formula is :— 


Thiocarbamide . 4 02. 31 g. 
Common alum . ei: ae ee 
Citric acid ‘ : =. 4 tee 
Water to. 4 Aa te 1,000 ccs, 


In very bad cases of fogging, this solution 
may be used without dilution ; but in ordinary 
cases one part stock solution to one or two parts 
of water will be preferable. 

Fogging from over-exposure, or from exposing 
the plate too freely to the dark-room light, is 
best treated by Farmer’s reducer, this consisting 
of “‘hypo”’ and potassium ferricyanide. 

Fogging by exposing the plate too much 
during development or in loading the camera is 
most difficult to treat successfully. (See also 
‘‘Exposurte, Incorrect.’’) 


FOGGED PRINTS, TREATMENT OF 

Fogged prints are generally not worth the 
trouble of treatment, excepting bromide and 
gaslight paper prints in which the white parts 
are degraded through the paper being stale. 
In all other cases the prints should be thrown 
away and replaced by new ones. The treat- 
ment should be the same as that given for plates 
showing development fog, or fog arising from 
the plates being stale. (See ‘‘ Fogged Nega- 
tives, - Treatment of.”’) The thiocarbamide bath 
should be used, but the solution should be 
more dilute. In most cases, 1 part of the 
stock solution already given should be taken 
and 3 parts of water added. The thiocar- 
bamide bath should be used after fixing and 
well washing the print. 


FOLDING CAMERA (Fr., Chambre pliante, 
Chambre folding; Ger., Falte-kamera, 
Klapp-kamera) 

Any camera made to close by folding, as 
opposed to studio and process cameras, which 
do not close in this way, and to box-form hand 
cameras. A folding hand camera is commonly 
understood to be of a specially light and portable 
construction, although the term is used very 
indefinitely. A style of hand camera in which 
the front extends on four struts is known in 
Germany as a “‘klapp”’ camera. (See also 
**Hand Camera.’’) 


FOREGROUND 

The part of a subject nearest the spectator. 
The term is stretched to include water. As 
foreground objects are naturally seen with the 
greatest clearness, the treatment of this part of 
a picture demands careful attention. Especially 
is this the case with stereoscopic pictures. Fore- 
ground objects may be brought into greater 
prominence if the camera is lowered consider- 
ably, especially when (as in the case of a group 
of flowers) they are intended as the subject of 
the picture. 
near foreground and also the distance quite 
sh without considerable stopping-down of 
the lens; and in such a case the top of the 
camera back may be swung away from the lens. 
If there is to be lack of definition anywhere in 
the picture the foreground is usually the last 
place where it is permissible. 


267 


It is sometimes difficult to get a» 


Formosulphite 


FOREGROUND SHUTTER (Fr., Obdtuvateur 

des devants ; Ger., Vortergrund-verschluss) 

A shutter designed to give a longer exposure 

to the foreground of a landscape, or similar out- 

door composition, than to the sky, thus enabling 

both to receive a more correct exposure than 
would otherwise be the case. 


FOREIGN PLATES, ETC. (For sizes, see 
*““ Sizes of Plates and Papers.’’) 


FORMALINE, FORMALDEHYDE, FORMIC 
ALDEHYDE, FORMIC ANHYDRIDE, 
OR ANTIPYR (Fr., Formol ; Ger., Alde- 
hyde formique, Formalin, Formaldehyd) 

Best known as formaline. Ordinarily it is 
met with in aqueous solution, which is prepared 
by passing the vapour of methyl alcohol mixed 
with air through a heated tube containing 
copper gauze. The liquid is colourless, has a 
characteristic smell, and, as obtained com- 
mercially, contains about 40 per cent. of formalde- 
hyde. Formaline vapour attacks the mucous 
membranes of the eyes, nose, and throat, and 
causes intense irritation. 

Photographically, it is used chiefly for harden- 
ing gelatine films, it replacing and being safer 
than alum. A suitable strength is 10 per cent., 
and it may be used immediately after fixing 
for both negatives and prints. It has also 
been suggested as a constituent of developers, 
the most useful formula being— 


Hydroquinone , 40 gts. 16 g. 
Sodium sulphite Bae (+) iat 160 ,, 
Formaline 50 drops 20 ccs. 
Water to. 5 Oz. T0000 y; 


The above is a one-solution developer ready for 
use, no bromide or alkali being required when 
formaline is present. The above developer is 
suitable for negatives of black-and-white draw- 
ings, or for giving strong contrasts in other 
subjects. 


FORMIC ACID (Fr., Acide formique; Ger., 
Ameisensadure) 

Synonym, hydrogen carboxylic acid. H COOH. 
Molecular weight, 46. A clear liquid obtained by 
distilling oxalic acid with glycerine. It is a 
dangerous caustic, and must be handled very 
carefully. It was used in the old wet-plate 
days, and has been recommended as a preserva- 
tive for pyro, but whilst a good preservative, 
the addition of an alkali turns the solution 
muddy and black. 

In process work, formic acid is sometimes used 
instead of acetic acid for the stripping of wet 
collodion negatives. Its disadvantage is that it 
is injurious to the hands. 


FORMOSULPHITE (Fr., Formosulfite; Ger.» 
Formosulphite) 


One of Messrs. Lumiére’s patented products, 
which takes the place of an alkali in the developer. 
It is sold in the form of a white crystalline 
powder, and, as its name suggests, is a prepara- 
tion of paraformaldehyde, sodium sulphite, and a 
small quantity of an alkaline bromide. It acts 
also as a preservative, prevents stain, and hardens 
the film. 


Formyl Chloride 268 


FORMYL CHLORIDE OR TRICHLORIDE 
(See “ Chloroform.’’) 


FOTHERGILL PROCESS (Fr.,"Procédé Fother- 
gill; Ger., Fothergill’’s Prozess) 

A. dry process introduced by Thomas Fother- 
gillin 1858. The plate having been collodionised 
and sensitised in a neutral silver nitrate bath, 
as usual in the wet-plate process, was washed 
with rain water and allowed to drain for about 
half a minute. Some plain albumen, obtained 
by well beating the white of 1 egg with 2 drms, 
of water, and allowing to subside, was then 
poured on the collodion film, and, after remain- 
ing for thirty seconds, was washed off under a 
gentle stream of rain water, sufficient remain- 
ing in the pores of the collodion to answer the 
purpose of preserving its sensitiveness. The 
plate was then allowed to dry and was fit for use. 
Such plates would keep some time, and could be 
exposed dry without previous preparation. 


FRAME (Fr., Cadre; Ger., Rahmen) 

The selection of a suitable frame for a finished 
print is an important matter. Fortunately, the 
special demands of photographers in this respect 
have been fully met, and there is now no lack 
of choice in appropriate frames. It must be 
remembered that the chief purpose of a frame, 
with or without a mount, is to isolate the picture 
from its surroundings. Therefore, a frame 
defeats its own end when it attracts attention 
from the print to itself. For this reason an 
ornate, or so-called “fancy ” frame, is generally 
unsuitable. The great majority of photographic 
prints are seen to best advantage in a simply 
designed frame of a dark colour. The various 
mouldings may be roughly classified into those 
that are flat and practically flush with the 
picture, those that throw it forward, and those 
that throw it back. If the print is framed close 
up, that is, without showing any margin, a 
wide moulding is generally best. A narrow one 
in such a case does not adequately isolate the 
print, and has a “‘ skimpy ” effect. On the other 
hand, a mounted print demands a much narrower 
moulding. The more mount there is the narrower 
may the moulding be, as the mount and frame 
may be regarded as a whole. 

Gold frames, and those with a highly varnished 
surface, are not often suitable. Far more effec- 
tive, as a rule, are well-made frames of good 
solid oak, stained brown or black, and polished 
by friction with a brush or a rough cloth, or by 
the sparing application of beeswax and turpen- 
tine. (See also “ Framing.’’) 


FRAMES, PRINTING (See “ Printing Frames.”’) 


FRAMING 


In addition to the actual selection of a suit- 
able frame for a photograph (see “Frame ’”’), 
there are one or two other points to take into 
account. First comes the question of the glass. 
This should not only be free from flaws and 
waviness, but it should be as colourless as possi- 
ble. If a sheet of the usual picture-framer’s 
glass be laid down, so as to cover half of the 
print only, a great difference will be noted 
between the covered and uncovered halves. N ot 
only is the colour of the print affected, but there 


Freezing or Cooling Mixture 


is a marked alteration in the values. Generally 
the tones are degraded or flattened, especially 
in the case of delicate grey prints. When a 
clearer glass cannot be used, the print should be 
kept somewhat brighter than it is intended to 
appear in its framed state. When the glass is 
placed in the frame it is well to run a narrow 
fillet of paper round the edge, pasting it down to 
the glass and the sides of the rebate. Take care 
that it does not show from the front, its object 
being merely to keep out dust. The backboard 
having been bradded securely down, glue or 
paste brown paper over the entire back. 


FRAUNHOFER LINES 


When a solar spectrum is viewed in a spec- 
troscope with a very narrow slit it will be seen 
to be crossed by thousands of transverse dark 
lines. The most prominent of these were named 
by Fraunhofer according to the letters of the 
alphabet, and are now called by his name. 
No matter what the dispersing medium may be, 
prism or grating, these lines always fall in exactly 
the same colour; they are therefore extremely 
convenient ‘ milestones” or data for naming 
any colour, and enable one to define a colour 
exactly. For instance, the term “ yellowish 
green ’’ conveys no strictly definite idea ; whereas 
the term “a yellowish green like p 4 E’’—that 
is, midway between the Fraunhofer lines p 
and E—indicates a definite and fixed tint, The 
cause of Fraunhofer lines was determined by 
Kirchoff and Bunsen, who discovered that any 
substance in a state of incandescent vapour 
absorbed exactly those rays which it emitted 
when in a state of luminescence, For example, 


if a pellet of metallic sodium is burnt in an elec. : 


tric arc it emits two dazzling orange-yellow 
rays, known generally as the p lines; but if 
the light thus emitted is allowed to pass through 
a cloud of somewhat cooler sodium vapour these 
brilliant yellow lines instantly become black— 
that is to say, their light is absorbed. This 
fundamental law applies to all substances, and 
by its aid it has been possible to detect the 
elements burning in the sun and in still more 
distant stars. (See also “ Spectrum.’’) 


FREEZING OR COOLING MIXTURE (Fr., 
Mélange réfrigévant ; Ger., Kaltemischung) 
A mixture which, by absorption of heat in 
liquefying, produces a low temperature. It is 
largely used in hot countries, and sometimes in 
England during hot weather, to cool solutions, 
particularly for use with gelatine plates and 
papers. The ordinary “hypo ” fixing bath is 
itself a cooling mixture, for when freshly mixed 
the temperature of the water falls considerably. 
The most common freezing mixtures are the 
following :— 


Proportions Temperature 
by Weight Produced 
Snow or pounded ice 2 
Common salt (sodium chlor- —-4°R, ) —28", 
ide) 7 a ve Ok 
Snow ws a ae aS 
Crystallised calcium chlor- —54°F. —48°C, 
oan ak wa ‘mee 
ater E: ra 09 aE ° ° 
et Nitrate “eee: } S°F, —15°C, 
Sodium sulphate .. - 8 apy ° 
Hydrochloric acid oo 5 } tn4; Conia 


French Chalk 


A good method of lowering the temperature 
of solutions is to place the bottles containing 
them in a freshly made “‘hypo’”’ bath. 


FRENCH CHALK (See “ Chalk, French.’’) 


FRILLING 

A trouble to which negatives are liable while 
undergoing treatment in the various solutions ; 
the edges of the gelatine film leave the glass plate 
and are cockled. It is due to the uneven temper- 
ature of the solutions, excess of soda or other 
alkali in the developer, handling the negatives 
with the warm fingers, the use of strong fixing 
solutions, or to rapid washing, the water being 
allowed to impinge upon the edges of the plates 
in such a way as-to lift the films. Frilling may 
be prevented by hardening the film before or 
after development with formaline, or a com- 
bined fixing and hardening bath may be used. 
If no precautions are taken and the gelatine 
is found to be frilled, it may be more or less 
remedied by treating with methylated spirit. 
Frilling is allied to the far more common defect 
of blistering, and the remedies given under a 
separate heading for the latter apply equally 
well for the former. Frilling often appears on 
print-out papers when they are torn, as, for 
example, when a half-plate piece is torn into 
halves for use as quarter-plates. | Printing papers 
should always be cut clean, because rough edges 
allow the water to get easily under the films, 
so causing frilling. 

Two old-fashioned but serviceable methods of 
preventing plates from frilling may be mentioned. 
One is to soak the dry plate before development 
in a saturated solution of Epsom salts, and the 
other is to rub a wax or tallow candle round the 
exposed dry plate on the film side, before wetting 
it with the developer. Neither of these, however, 
is as reliable as immersion in a 10 per cent. solu- 
tion of formaline. (See also “‘Hardeners’”’ and 
** Blisters.’’) 


FRONT, CAMERA (Fr., Planchette d’objectif ; 
Ger., Objektivbrett) 

That part of the camera which carries the 
lens. It should be provided with a rising and 
falling movement, and a cross movement is an 
additional advantage. In field cameras, it 
should preferably also be arranged to swing, in 
order that the lens may be tilted if desired with- 
out needing to incline the camera. The fronts 
of large cameras are commonly furnished with a 
removable panel for the lens, an arrangement 
which, by the employment of several panels, 
permits various lenses of different sizes or foci 
to be used interchangeably on the same camera, 
(See also “‘ Cross Front,” “‘ Detachable Front,” 
** Rising Front,” and “‘ Swing Front.’’) 


FROST SCENES 

The photographing of frost scenes is dealt 
with under the heading ‘‘ Snow and Hoar Frost 
Photography.” Frost on window-panes may be 
successfully photographed by placing a black 
cloth outside the window at an angle of 45° and 
photographing the frost from the inner side. 


269 


Furnell’s Developer 


F.R.P.S. 


Fellow of the Royal Photographic Society. 
The Fellowship was instituted January 1, 1895, 
and is open to those who, being already members, 
satisfy the Council of their ability in, or con- 
tributions to, any branch of photographic work, 
an annual subscription of two guineas being 
payable. 


FULL APERTURE 


When no stop is used, a lens is said to work 
at “open aperture” or “full aperture.” 


FULMINATING COTTON 


Another name for gun-cotton (which see). 
Sometimes used in flashlight photography. 


FUMING 


Photographically, the exposing of albumen 
paper to the fumes of ammonia ; paper so treated 
gives brighter prints and tones to richer colours 
more easily. The sensitive paper to be fumed is 
pinned to the inner side of a box lid;. in the 
bottom of the box is placed liquor ammoniz in 
a saucer, or it is sprinkled upon blotting-paper. 
The box is then closed, and the paper exposed 
(in the dark, of course) to the action of the 
ammonia fumes for about ten minutes, or longer 
if the weather is cold. Fuming is now almost 
obsolete, but at one time it was recommended 
for papers other than albumen, and even for 
plates. 


FURNELL’S DEVELOPER 

A developer widely advocated about 1890 for 
positive work; it is claimed to keep for years, 
allow great latitude in exposure, give clear glass 
shadows, and not frill the film. 


No 1:— 
Sodium sulphite « §0 gts. IO g. 
Powdered alum SPIO <2, si 
Distilled water . eZ OB. 250 ccs. 
Dissolve, filter, and then add— 
Pyro : : . 24 gts, 4°8 g. 
Sodium nitrate poet ge Vie Se 


This is made up as a stock solution, and it will 
keep indefinitely. 


No. 2:— 
Liquor ammoniz (‘880) 1} drms. 75, CCE, 
Ammonium bromide 30 grs. 6 g. 
Distilled water to 15. dims, 150 ccs. 


To develop, take $ oz. of the No. 1 (pyro) solu- 
tion, made up to 2 oz. with water, and add 10 
drops of the No. 2 (ammonia) solution, and apply 
to the plate, adding more of the latter if neces- 
sary. After development, do not wash but rinse 
in a saturated solution of alum, then wash and 
fix in the following bath, after which wash and 


dry :— 


Sodium hyposulphite 2 oz. 220 g. 
Sodium carbonate . 4,, Bae 
Alum (saturated sol.) 4,, 50 ccs. 
Water to ° ye 1? Sa 1,000 ,, 


G 


Y (See ** Gamma.) 


GAEDICKE’S INTENSIFIER 
One of the silver intensifiers, the formula 


being :— 
Ammon. sulphocyanide 100 grs. 46 g 
Silver nitrate : EAR ae 22°:,} 
Sodium sulphite SOO 2, 230 ';, 
“Hypo” : ‘ 100° |. 46 ,, 
Potassium bromide - Cees ae 
Water 5 oz 1,000 ccs, 
To prepare for use, mix as follows :— 
Stock solution as above 48 drops 100 ccs, 
Water to. . . 102!) TjO0G +, 
Then add— 
Rodinal : 3 - 16 drops 33 ccs. 


Immerse the negative therein until intensified 
and then wash. 


GALL (See ‘“ Ox-gall.’’) 


GALLATE OF IRON PROCESS 

Better known as the ‘Ink Process” (which 
see). The term has been loosely applied to other 
iron processes of printing. 


GALLIC ACID (Fr., Acide gallique ; 
Gallischsdéure) 

Occurs in fine, silky, yellowish crystalline 
needles. C,H, (OH); COOH H,0. Solubility 
I per cent. in cold water, 33 per cent. in boii- 
ing water. Largely used in the early days of 
photography as a developer for paper, nega- 
tives, and it was with this acid that Talbot in 
1835 made some important discoveries in con- 
nection with the latent image. It is occasion- 
ally used in modern processes, as, for example, 
in the development of P.O.P., intensification of 
collodion and gelatine plates, and as an ingre- 
dient in the ferrous citrate developer for chloride 
plates. 

Gallic acid is often used by lithographers for 
preparing the surface of zinc plates for printing, 
instead of the nutgall decoction recommended 
by the old workers; the effect is the same, and 
the trouble of preparing the decoction is saved. 


GALLO-NITRATE OF SILVER PROCESS 
Another name for the old calotype or talbotype 
Paper process, in which paper was sensitised 
with silver nitrate, immersed in potassium 
iodide, washed, dried, exposed, and developed 
with a mixture of silver nitrate, gallic, and 
acetic acids and water. (See “‘ Calotype.’’) 


GALLS (NUTGALLS) 

In zincography—lithographic printing from 
zinc plates—a decoction of nutgalls, mixed with 
gum arabic solution, is used for preparing the bare 


Ger., 


parts of the zinc so that they repel the greasy 
ptinting ink used for rolling-up. To make the 
decoction, steep 4 oz. of nutgalls in 3 quarts of 
water for twenty-four hours, and then boil up 
and strain. For use, add 3 pint of this solution 
to ¢ pint of gum solution, of the thickness of 
cream, and 3 drams of a solution of phosphoric 
acid, 


GALVANOGRAPHY 

Under this name there have been put forward 
several processes based on the idea of painting 
on a silvered copper plate with oil colour in thick 
masses so as to give relief. When dry, or nearly 
so, the surface is dusted with finely powdered 
blacklead to make it electro-conductive, and a 
thick copper shell is deposited on it, "This is 
subsequently used as an intaglio printing plate. 
A process of this kind was patented by Prof, 
Herkomer and Henry T. Cox in 1898. The basis 
of the method was described by Franz von 
Kobell, of Munich, as early as 1842. 


GALVANOGRAPHY, PHOTOGRAPHIC 

A process of utilising a gelatine relief as a 
mould for making electrotypes. Several in- 
ventors have adopted the title, but Paul Pretsch 
had probably the best right to it, His process. 
consists in coating a glass plate with gelatine 
containing bichromate, with a silver salt and 
other chemicals. When dry it is exposed under 
a transparency, and then immersed in cold water 
to dissolve out the unaltered chromium salts 
and cause those parts protected from the light 
to swell up in proportion to the tones of the 
picture. The high lights do not swell at all, and 
have no grain. The plate thus produced is, of 
course, am exact reverse of that required for 
printing. The surface is next made conductive 
with a metallic coating, so that an electro- 
deposit can be made upon it, thus producing a 
copper shell which can be backed up with type 
metal to form a printing plate. 


GAMBOGE (Fr., Gomme gulte; Ger.. Gummi- 
guit) 

Synonyms, camboge, gummi gutte. A gum 
resin obtained from several species of guttifere 
trees, occurring in bright orange lumps with 
conchoidal fracture; used as a colouring pig- 
ment, 

The coating of lithographic writing transfer 
paper is coloured with gamboge in order that the 
prepared side may be distinguished from the 
unprepared one. Gamboge has been recom- 
mended as an addition to Indian ink for drawings 
intended for photo-reproduction. 


GAMMA (Fr. and Ger., Gamma) | 
The term adopted by Hurter and Driffield 
define the gradation, or degree of contrast, of a 


270 


Gas Cylinders 


negative. Gamma infinity, or yoo, as it is 
usually written, is the ultimate density-giving 
power of the plate. (See ‘‘ Plate Testing.’’) 


GAS CYLINDERS (See “ Cylinders, Gas.’’) 


GASLIGHT PAPERS 

Papers coated with a chloride or chloro-bro- 
mide emulsion, which can be manipulated in weak 
gaslight. For suitable emulsions, see under the 
heading ‘“ Emulsions for Development.’ Gas- 
light paper (so called) is really a very slow bro- 
mide paper, and is developed, fixed and toned (if 
necessary) like bromide paper, except that the 
developer must be stronger, and the develop- 
ment is more rapid. Exposure can be made by 
putting the paper into contact with a negative 
which is held a few inches from a gas burner or 
good oil lamp, but development must not take 
place in a light equally strong or the print will 
be fogged; either the light must be turned 
down during development, or the operation 
must be carried out at some distance from the 
light or in a shadow. Artificial lights other 
than gaslight, or even very weak daylight, will 
serve equally well ; in fact, the common practice 
is to expose to the light of magnesium ribbon 
and develop by aid of weak artificial light. A 
metol-hydroquinone developer is usual, and this 
must be accurately prepared, particularly as 
regards the potassium bromide; too little 
bromide causes impure whites, while with too 
much the blacks will be of a greenish hue. 
Development should take place almost in- 
stantaneously. An acid fixing-bath is advisable, 
but not mecessary. The colour of the print 
depends on exposure and development; longer 
exposure and a weaker developer invariably 
produce warmer tones. With most papers a 
watm brown tone may be obtained by giving 
three times the normal exposure and diluting 
the developer with twice the bulk of water. 


GASLIGHT, PORTRAITURE BY 

The use of gaslight is possible for portraiture. 
With ordinary gaslight (without mantles), ex- 
posures are long even under the most favour- 
able conditions, the light being poor in violet 
tays and comparatively,non-actinic, Gaslight has 
advantages for isochromatic work, as without a 
yellow screen it gives practically the same result 
as daylight with a screen, isochromatic plates 
being used in both cases. With a very rapid 
plate, and the lens stopped down to f/8, the neces- 
sary exposure with two gaslights (not incan- 
descent) 3 ft. from the sitter would be about 
two minutes. Particular care is necessary in 
posing, using a reflector, and in development, 
as the results are bound to be a trifle hard and 
** contrasty.”’ 

Incandescent gaslight is better for portraiture, 
as a full-size mantle gives an illumination of 
about sixty candle-power when at its best, and 
is about one and a-half times as effective 
photographically as a gas flame of the same 
visual intensity, because of the whiteness of the 
light and its richness in the blue or actinic rays. 
The exposure depends, of course, upon the num- 
ber of burners. The special fittings obtainable 
from factors are in the form of brackets containing 
a score or more lights, which make possible quite 


271 


Gelatine 


brief exposures—say one or two seconds; but 
an enormous amount of heat is produced. Fair 
results may be obtained with one or more 
ordinary domestic burners, but the exposure is 
somewhat long, a minute at least, with two 
lights near to the sitter, a very rapid plate, and 
the lens at //8. 

It will be noted that ail gaslights are in- 
candescent, the light in a plain flame being 
produced by heating particles of carbon to in- 
candescence ; but it is convenient to adopt here 
the ordinary nomenclature by which the term 
““incandescent ’”’ is restricted to burners of the 
Bunsen type, fitted with mantles of rare earths. 

Acetylene outfits for portraiture are similar 
to the incandescent gas fittings in arrange- 
ment. The light is very actinic, and as a rough 
guide it may be said that when using fourteen 
acetylene lights, a rapid plate, and a lens at //8, 
an exposure of about five seconds is required in 
an ordinary room; the distance of the lights 
from the sitter greatly affects the length of the 
exposure. (See also “ Artificial Light, Photo- 
graphy by.’’) 


GAUGE, PRESSURE 


The lanternist ascertains the contents of gas 
cylinders by means of a gauge. He may know 
that the cylinder is of 20 cubic feet capacity, and 
the full cylinder gives a gauge pressure of 120 
atmospheres; after the exhibition, the gauge may 
indicate, say, 50 atmospheres. Then the content 
oe X20 es 28 = 84 cubic feet. 

A pressure gauge is used on the motor aero- 
graph pump, the degree of pressure being indi- 
cated in pounds per square inch on a circular 
dial. With the aerograph foot pump a simple 
form of pressure gauge is used, consisting of a 
U-shaped tube filled with a coloured fluid, one 
end being closed and the other attached to the 
air reservoir. As the pressure varies it is indi- 
cated by marks on a scale placed behind the 
tube. 

On the large vacuum and pneumatic frames 
used by process workers there is generally a pres- 
sure gauge, reading in pounds per square inch 
on a circular dial. 

The Levy acid-blast etching machine has a 
gauge consisting of a column of mercury in a 
glass tube, communicating with a U-tube in the 
iron casting of the gauge. As the pressure 
increases or decreases the mercury rises or falls, 
and the pressure in pounds per square inch is 
read on a scale alongside the glass tube. 


GAUSS POINTS (See “ Nodal Points.’’) 


GELACOL 

A preparation of gelatine treated with acetic 
acid to destroy its setting property. It is used 
for coating glass plates with a substratum, par- 
ticularly in collodion emulsion work. 


GELATINE (Fr., Gélatine; Ger., 
Gelatin) 

A colloid of extremely complex nature, con- 
taining carbon, hydrogen, nitrogen, and oxygen, 
with a small proportion of sulphur. It is known 
commercially in fine shreds or thin, flat sheets, 
marked with the diamond pattern of the strings 


equals 


Gallerte, 


Gelatine 


on which it is dried. Photographic gelatine is 
usually prepared from selected hides, whereas 
inferior sorts are prepared from bones, tendons, 
and cartilages. It is insoluble in cold water, 
which it absorbs and then swells up to a slimy 
mass; it is soluble in all proportions in hot 
water, but insoluble in alcohol and ether. The 
principal constituents are two substances known 
as glutine and chondrine; the former is not 
precipitated by the alums, whilst the latter 28, 
and gelatines rich in chondrine are the best 
for photographic purposes. A simple test for 
this is to add to a warm 1o per cent. solution of 
gelatine an equal volume of a saturated solution 
of chrome alum, when the solution should in- 
stantly set to a jelly. It is only possible to 
indicate the general characteristics of a gelatine 
suitable for photographic purposes, as the true 
test of its suitability is to make a practical trial 
with a small batch of emulsion. A good gela- 
tine should absorb not less than six times its 
weight of water, and not much more than twelve 
or fifteen times, 

There are three kinds of photographic gela- 
tine: hard, medium or middle hard, and soft. 
Hard gelatines should not melt below 82° F. 


c= 


Device for Determining Melting Point 
of Gelatine 


(nearly 28° C.); if they do not melt at 83° F, 
(31° C.), there is a risk of their having been 
hardened with alum. Soft gelatines should 
melt at from 62° to 75° F, (say 17° to 24° CG). 
A I per cent. solution should set to a jelly when 
cooled down to 56° F. (133° C.), and remain 
without any sign of putrefaction for twenty- 
four hours. 

The determination of the melting point is 
somewhat difficult, anv Child Bayley has sug- 
gested an excellent practical device here shown 
in the testing position. This may be made 
of copper or zinc, and the sloping portion is 
to prevent heat from the Bunsen burner passing 
direct to the front of the tank. Across the 
front of the tank should be scratched a line 
about 1 in. from the top, and on this line should 
be placed some discs of gelatine, Gummed labels 
are cut into strips about f in. wide and about 
1} in. long, and their ends are then gummed 
together, with the gummed surface outside, so 
as to form rings, The tank should be placed 
with the front and marked surface up, and the 
paper rings placed on the line and then carefully 
filled by means of a pipette with a warm to per 
cent. solution of gelatine. When the gelatine 
is thoroughly set, the tings should be cut down 
with a sharp knife and stripped off, and the 
tank set upright and filled with cold water, and 


272 


Gelatine, Bichromated 


this heated by means of the Bunsen burner. 
The discs must be carefully watched, and when 
they begin to melt and run down over the line 
the temperature should be noted. A mean of 
six trials may be taken as correct. 

Another method is to use a thermometer in a 
very narrow test tube, just 1 mm. (s; in.) wider 
all round than the thermometer bulb, which 
should be of elongated shape. ‘Then fill the tube 
with the gelatine solution and, while hot, 
immerse the thermometer well into the tube, 
and set. Afterwards place the tube in warm 
water, and gradually raise the temperature; then 
when the gelatine melts, the tube will drop off, 
and the temperature can be noted. 

Gelatine is used for preparing baryta paper, 
for emulsions, both negative and positive, in 
collotype, photogravure, and other photo- 
mechanical processes, and it is the chief in- 
gredient of an excellent mountant. 

Solutions of sulphocyanides and barium 
chloride dissolve gelatine in the cold, as do also 
acetic, oxalic, hydrochloric, and sulphuric acids. 
Zinc chloride and chloral hydrate destroy its 
setting power. The setting is increased by the 
alums, magnesium sulphate, and numerous other 
Salts. It forms a compound, gelatinate of 
silver, which is sensitive to light, with silver 
nitrate. 

In process work, gelatine has numerous uses 
—namely, for coating collotype plates, for pre- 
paring photo-lithographic paper, for the carbon 
tissue in the photogravure process, for the making 
of gelatine reliefs, for use as a substratum on 
glass plates, for the making of films for shading 
mediums, for making litho-transfer papers and 
films for tracing, for stripping negative films, 
for making colour filters, for glazing prints, etc. 
Particulars of these applications and uses are 
given under the respective subject headings, 


GELATINE, BICHROMATED 

Gelatine treated with an alkaline bichromate 
forms the basis of the carbon process and of all 
photo-mechanical printing methods. Fish-glue 
is employed in some processes, but that is a sub- 
stance closely allied to gelatine: and other 
colloids are sometimes substituted, as in the 
gum-bichromiate process. Gelatine, in its nor- 
mal condition, will absorb cold water readily, 
and dissolve easily in hot water. Gelatine 
treated with an alkaline bichromate retains these 
qualities if kept in the dark; but if exposed to 
light, it no longer absorbs cold water, or swells 
in consequence, and it also becomes insoluble, 
These properties are utilised in different printing 
methods. In the carbon process, and in some 
photo-mechanical methods, an image in gelatine 
is produced by exposing a film of bichromated 
gelatine under a negative, and then dissolving 
away those parts on which the light has not 
acted by means of hot water, In others, a 
gelatine relief is produced by means of the 
unequal swelling of a gelatine film that has been 
exposed under a negative when soaked in water. 
Details of the various processes in which these 
qualities are utilised are given under their 
respective headings. 

In process work, many processes depend on 
the properties of bichromated gelatine. Among 
these may be mentioned collotype, photogravure, 


Gelatine Emulsions 


photo-lithography, and photo-relief. For the 
half-tone process gelatine has not been found 
so satisfactory as fish-glue, the latter having no 
setting property, and being easily developed 
with cold water. An attempt was made of late 
to utilise for half-tone a gelatine in which the 
setting property had been destroyed, but it was 
found to be more subject than fish-glue to changes 
of temperature, and also liable to become putrid 
very readily. 


GELATINE EMULSIONS (See ** Emulsion.’’) 
GELATINE MOUNTANTS (See “Mountants.’’) 


GELATINE PAPERS 

Printing papers which are coated with gelatine, 
which acts as a vehicle for the silver salts. All 
bromide and gaslight papers, and most makes 
of ordinary P.O.P., are gelatine papers. Some 
makes of P.O.P. are coated with collodion. 
Nearly all self-toning papers have collodion 
emulsions, but a few have gelatine. Gelatine 
papers are sticky when wet, and the emulsions 
dissolve in hot water. 


GELATINE PLATES AND FILMS 

Glass plates or celluloid coated with gelatine 
emulsions, as distinguished from  collodion 
plates. 


GELATINE RELIEFS 

Probably more ingenuity has been displayed 
in devising processes for making gelatine reliefs 
to serve as printing surfaces than in any other 
form of photo-mechanical work, and yet there 
is not one of these processes that is in regular 
commercial use at the present day. These pro- 
cesses date from the experiments of Fox Talbot 
and Poitevin. In general the basis of the pro- 
cess is the preparation of a thick film of bichrom- 
ated gelatine on plate glass, exposing it under a 
negative or positive when dry, and developing 
with warm water so that the unexposed parts 
wash away, leaving those portions standing that 
have been acted upon by light. The relief is 
hardened with alum or other agents, and dried. 
(This is the “ Wash-out Gelatine Process,” 
which see.) In some processes, however, the 
unaltered gelatine is not washed away, but is 
allowed to swell up, and thus form a matrix 
for casting in plaster. (See ‘‘ Swelled Gelatine 
Process.’’) 

The foregoing were chiefly used for line repro- 
duction processes, but others are intended for 
making half-tone reliefs. Dallastype and Dallas- 
tint, and Pretsch’s photo-galvanography are 
ptocesses of the kind that are described under 
separate headings; and Woodbury also devised 
a process of this nature for typographic printing. 
The half-tone image is either formed by printing 
through a screen, or by reticulating the surface 
of the gelatine. In Woodburytype (which see) 
the gelatine relief is utilised, but in an essentially 
different manner from the foregoing; pigment 
is introduced into the film, and development is 
similar to that of carbon tissue. Stannotype is 
a variation of Woodburytype. Photo-filigrane 
(see “‘Filigrane’”’) is another process depending 
on a gelatine relief. (See also “‘ Acrograph,”’ 
““Leimtype,” ‘‘ Mosstype,” ‘‘ Stannotype,”’ etc.) 

18 


273 


Geological Photography 


GELATINEGRAVURE 

Transparent gelatine is placed over a photo- 
graph, and a drawing made byscratching. When 
this is complete the lines are filled with litho- 
graphic transfer ink thinned with turpentine 
and applied with a dabber. Printing is done by 
running the gelatine through a roller press in 
contact with paper. 


GELATINO - BROMIDE PAPERS 
PLATES 
Papers or glass plates coated with gelatino- 
bromide emulsions. 


GELATINO-BROMIDE PROCESS (Fr., Géla- 
tino-bromure ; Ger., Bromsilber gelatin) 

A term used in the early days of dry-plate 
photography to distinguish the method of manu- 
facture of the emulsion from collodion It is 
now also used to include bromo-iodide plates. 


GELATINO-CHLORIDE PAPER 
Paper coated with an emulsion of silver 
chloride in gelatine. 


GENRE WORK 

The word “ genre’ comes through the French 
from the Latin “genus,” a kind. In painting 
it has been used to signify figure subjects of a 
homely or domestic character, generally engaged 
in their ordinary occupations. The term has 
been adopted to signify the same subjects 
treated photographically. Similar considera- 
tions apply as in dealing with single figures and 
groups. There are the same difficulties of 
securing satisfactory pose and arrangement, and 
a suggestion of natural action. The “setting ” 
of the figures and the choice and arrangement 
of the accessories also play an important part. 
Careful studio arrangements and the employ- 
ment of good models have frequently led to the 
production of excellent genre pictures, but the 
best and easiest way is to study and treat the 
real subjects and their ordinary surroundings 
both in and out of doors. The works of some 
of the painters of the Dutch school offer very 
fine examples of the effective treatment of genre 
subjects. The thing to aim at is harmony 
and unity. (See also “‘ Figure Studies.’’) 


GEOLOGICAL PHOTOGRAPHY 
Photography as applied to geological inves- 
tigation may be roughly classed under the 
following headings: (1) Photographs showing 
plains, valleys, escarpments, base levels, moun- 
tains, lakes, rivers, glaciers, etc., taken for the 
purpose of illustrating the origin of landscape, 
and the action of atmospheric and other pro- 
cesses of denudation. (2) Photographs of the 
faces of cliffs, quarries, railway cuttings, and 
other exposed surfaces, to show the way in 
which strata have been laid down, and changes 
which have taken place producing unconformity, 
overfolding, faults, dip and strike, anticline and 
syncline, crushing, cleavage, and joints. (3) 
Photographs of fossil remains, both in situ and 
after cleaning, to show the types of animal and 
plant life existing during the formation of the 
strata in which their fossil remains are embedded. 
(4) Photo-micrographs of thin sections of rocks, 
showing their structure, composition, and any 


AND 


Germeuil-Bonnaud 


minute animal and plant remains that may be 
present. 

For most geological photography, a good stand 
camera, having a long extension of bellows, 
swing back, and rising front, will be found most 
serviceable. A good lens is all-important, as 
the value of a geological photograph depends 
upon its perfect clearness and sharpness of 
detail. The lens should be provided with a deep 
hood for use in the field, which will prevent 
flare, and flat, foggy-looking negatives, caused 
by reflections and rays of light falling obliquely 
on the front surface of the lens. The tripod 
should be substantial and rigid, so that there 
will be no fear of vibration during exposure, 
for it is always best to stop down the lens and 
give a full-time exposure, so that a crisp, sharp 
negative, full of detail and gradation, may be 
obtained. It is often desirable when photo- 
graphing a portion of the face of a cliff, or part 
of the strata laid bare in a quarry or railway 
cutting, to include in the photograph some 
familiar object of which the size is well known, 
to act as a kind of rough scale by which one may 
judge the relative thickness of a deposit, or 
the size of a fossil seen im situ. For this pur- 
pose, some workers use their geological hammer, 
but as hammers vary a good deal in size and 
shape, it is much better to include a twelve- 
inch or two-foot rule. Orthochromatic plates 
should always be used. F. M-D. 


GERMEUIL-BONNAUD 
(Powder) Process.’’) 


GHOST IMAGES IN LENSES (See “ False 
Images, or ‘ Ghosts.’’’) 


GHOST PHOTOGRAPHY 
Photography.’’) 


GIFFORD’S SCREEN 

A so-called monochromatic light screen, made 
by immersing a slip of cathedral green glass, 
which is of bluish green tint, in a solution of ani- 
line green. It is used in photo-micrographic work, 
and passes a spectral band about E in the green. 


GIGANTOGRAPHY 

A process of making enlarged half-tone nega- 
tives for poster printing. Two cameras are 
required—one a small one, according to the size 
of the original image, and the other large enough 
to take the enlarged negative. The lens of the 
small camera is connected to an aperture in the 
front of the large camera, on the principle of the 
usual enlarging camera. An evenly graded 
transparency, thin but full of detail, is placed in 
the dark-slide of the small camera, the shutters 
drawn out, and the slide placed in position. The 
half-tone screen is placed in its holder in front 
of the positive, and the distance of the screen is 
set proportionately to the extension of the 
camera to secure the desired enlargement. A 
powerful light is reflected through the positive 
by illuminating with arc lamps a sheet of white 
paper placed behind it. The image is then 
focused, and the ruled screen adjusted until the 
desired dot image is obtained. The advantage 
of the process is that it saves the necessity of a 
very large and expensive ruled screen. 


(See ‘“‘ Dusting-on 


(See “‘ Psychic 


274 


Glass 


GILLOTAGE 

The earliest process of line zinc etching, in- 
vented by Charles Gillot, of Paris, and patented 
in France in 1850; known as panikonography, 
or the French or Parisian method of zinc etch- 
ing. The principle of the method is that an 
image in lithographic ink on zinc is strengthened 
for acid resisting by repeatedly rolling up with 
ink and then dusting with resin, the plate being 
heated to melt the resin, so that it runs down 
the sides of the lines and protects them against 
undercutting by the acid. 


** GIPHANTIE ”’ 

A book written in 1760 by a French- 
man, Tiphaigne de la Roche, the title being 
an anagram of his own name. It contains a 
forecast of photography. One paragraph says: 
** You know that the rays of light reflected from 
different bodies form pictures, paint the image 
reflected on all polished surfaces, for example, 
on the retina of the eye, on water, and on glass. 
The spirits have sought to fix these fleeting 
images; they have made a subtle matter by 
means of which a picture can be formed in the 
twinkling of aneye. They coat a piece of canvas 
with this matter, and place it in front of the 
object to be taken, The first effect of this cloth 
is similar to that of a mirror, but by means of 
its viscous nature the prepared canvas, as is 
not the case with the mirror, retains a facsimile 
of the image. The mirror reflects images faith- 
fully, but retains none; our canvas reflects 
them no less faithfully, but retains them all. 
This impression of the image is instantaneous. 
The canvas is then removed and deposited in a 
dark place. An hour later the impression is 
dry, and you have a picture the more precious 
in that no art can imitate its truthfulness.” <A 
still earlier writer, Fénélon, had a vision of 
photography, but did not so clearly express it; 
his book bears the title of “Un Voyage Sup- 
posé,” and was written in 1690. 


GISALDRUCK 

A photo-lithographic process, invented by 
B. Gisevius, of Berlin, for direct printing on 
aluminium without a negative. The actual draw- 
ing is printed through on to a sensitive film on 
the metal, and the negative image is converted 
into a positive. It resembles the Vandyke pro- 
cess (which see). 


GLACIAL ACETIC ACID (See “ Acetic Acid.”’) 


GLAISHER, JAMES 

Born in London, April, 1809; died at Croydon, 
February 7, 1903. Was for twenty-three years 
(1869 to 1874 and 1875 to 1892) president of 
the (now) Royal Photographie Society. He 
was largely responsible for the photographic re- 
cording instruments in Greenwich Observatory. 


GLASS (Fr., Glace, Verre; Ger., Glas) 
Ordinary glass is a fused mixture of silicates 
of calcium or lead with the silicates of sodium 
or potassium. While practically unaffected by 
acids, except hydrofluoric, it is attacked by strong 
alkalis, which dissolye out the silica. Some 
glasses are yellowed by prolonged exposure to 
light; this is frequently the case with old lenses. 


Glass 


Crown Glass is made usually from sand, lime, 
and a sodium salt, with sometimes lead oxide. 

Flint Glass contains potassium carbonate, red 
lead, sand, and saltpetre. It is easily fusible, 
and is not so suitable for chemical purposes, 
for which a soda-lime or potash-lime glass is 
preferable. 

Opal Glass is obtained by fusing an oxide of 
tin or zinc with the pot-metal; a “ flashed ’”’ 
opal, consisting of a thin opal layer united to 
plain glass, is also manufactured. 


Optical Glass first received specific attention. 


from Pierre Louis Guinand, of Les Brenets, in 
Switzerland (born 1748, died 1824), who obtained 
improved results by stirring the fused mixture 
with a rod of crucible clay. J. Fraunhofer (born 
1787, died 1826) succeeded in avoiding strie 
and in procuring glass of a uniform refractive 
index by the simple expedient of using larger 
pots for melting; he also investigated some of 
the optical effects resulting from variations in 
the ingredients and their proportions. In 1842 
a son of Guinand introduced boracic acid into 
the glass, which, however, did not then meet 
with favour. In 1851 Maes, of Clichy, produced 
a colourless and homogeneous zinc crown glass, 
containing zinc oxide and boracic acid; this 
was used in Charles Chevalier’s photographic 
objectives. lL. Seidel in 1856, and J. Petzval in 
1857, pointed out that new glasses, having a 
different relation between their refractive and 
dispersive powers to those then in use, were 
required for the perfection of the photographic 
objective, but it was not till Otto Schott and 
EB. Abbé began their joint work in 1881 that any 
real progress was made. In 1886 the famous 
Jena works were started by Schott, Abbé, and 
R. Zeiss, under a liberal subvention from the 
Prussian Government. Since then the pro- 
duction of optical glass of almost any required 
refractive or dispersive power has been rendered 
possible by the use of new chemical ingredients. 

People often talk loosely of the Jena optical 
glass, as if there were only one variety, although, 
as a matter of fact, several hundreds of different 
varieties of optical glass are known, these 
including all the ordinary flints and crowns, 
besides the special glasses that have made the 
manufacture of the modern anastigmats possi- 
ble ; it is these special glasses that are generally 
meant by the term “Jena glass.’ With the 
older makes of optical glass, increased refractive 
power was always accompanied by a high degree 
of dispersion, but in the new Jena glasses a 
very high refractive power is obtained with a 
comparatively low dispersion. 

' (For the optical properties of glass, see 
“‘ Lens.’’) 

Cements for Glass.—A cement for glass needs 
to be as colourless as possible, the best from 
this point of view being Canada balsam, which 
should be dried in an oven, allowed to cool, the 
glass gently heated, the remelted balsam thinly 
applied, and the surfaces brought together. This 
is the universal cement for lenses. Other ex- 
cellent cements (but not suitable for lenses) are 
water-glass, which, however, tends to roughen 
the glass, and an emulsion of gelatine in suf- 
ficient acetic acid to cover it, the process of 
digestion being assisted by standing the bottle 
in warm water. 


275 


Glass, Cleaning 


In process work, glass is an important material. 
To secure good contact between the negative 
and metal plate in direct printing, the glass 
must be flat, and plate glass is preferable, though 
for the general run of work a good selected 
sheet glass is used. Plate glass of about } in. 
thickness is used for assembling a number of 
stripped films on to one plate. For process 
printing-frames, thick plate glass is used up to 
17 in, thickness in the largest frames, and this 
glass must be well annealed in order to with- 
stand the strain of the pressure and the heat 
of the arc lamps used for printing. The glass 
must also be free from surface scratches and other 
imperfections which would show in the print. 


GLASS, CLEANING 

Glass for photographic purposes must be 
scrupulously clean. Glass upon which prints 
are squeegeed for glazing is best cleaned by 
soaking in very dilute nitric acid and scrubbing 
with soap and water; after drying, it is dusted 
over with French chalk and polished. When 
glasses are to be used for coating and sensitising, 
as in the wet collodion process, rouge or whiten- 
ing or fine tripoli powder mixed with methy- 
lated spirit to the consistency of thick cream 
is recommended; the paste is rubbed over the 
glass, rinsed off with water, and a final polish 
is given with chamois-leather. 

A good mixture for thoroughly cleaning glass 
for ordinary purposes is— 


Soft or rain-water . ~ ~f part 
Powdered pumice stone eh 
Chalk or whitening 14 ,, 
Liquor ammonie . : A pe ORE 


Apply with a piece of flannel, and polish with a 
soft rag, chamois-leather, or soft paper crumpled 


up. 

Fro clean films off old negatives, soak in hot 
soda-water for a few minutes, and scrub with a 
brush ; or, if they are not varnished, soak them 
for an hour or two in water made slightly acid 
with nitric acid; the films can then be rubbed 
off with a strip of wood, or placed in hot soda 
water and scrubbed. When the negatives have 
been varnished, it is necessary to use a strong and 
hot solution of common washing soda or caustic 
potash, and leave the negatives in this until cold, 
when the films will leave the glass. Do not let 
the caustic potash solution touch the fingers. 

In process work, in which collodion and collo- 
dion emulsion are used so largely, it is necessary 
to take great pains in cleaning glass. New glass 
is best soaked in a 5 per cent. solution of hydro- 
chloric acid contained in grooved lead - lined 
troughs; and it is then rinsed with plenty of 
water and polished with methylated spirit 20 0z., 
tripoli 10 0z., iodine 2 drams. Prepared chalk 
or whiting may be used instead of tripoli, and 
equal parts of methylated alcohol and ammonia 
instead of iodine. 

For removing collodion films from old nega- 
tives, nitric acid is generally used in the pro- 
portion of 1 oz. acid to 6 oz. water. A good 
film-removing pickle, free from fumes, consists 
of— 


Sulphuric acid : ~ 4°02, 2004CC8, 
Potassium bichromate . 4 ,, 220g. 
Water . » é LIVE TE EO OS: 


Glass, Etching on 


After treatment, swill and put in the draining- 
rack. Next, with a linen rag charged with 
whiting of the consistency of thick cream, rub 
well both sides of the partially dry negative 
glasses; then put into a clean bath composed 
of nitric acid 4 0z., water 40 oz. Finally, swill 
under a tap and then albumenise. 


GLASS, ETCHING ON (See ““Hyalography.’’) 
GLASS, GREEN (See “ Green Glass.’’) 


GLASS, PHOTOGRAPHS ON 

In 1848 Niepce de St. Victor produced photo 
graphs upon glass in the form of negatives, but 
glass as a support for photographs was suggested 
by Sir John Herschel in 1839. About 1850 
Archer produced positives on glass by the collo- 
dion process. 

Photographic negatives are now almost 
entirely upon glass or celluloid. Photographic 
positives on glass are produced in many ways, as 
described under the headings “‘ Lantern Slides,” 
** Window Transparencies,” etc. 


GLASS POSITIVES 

Photographs on glass, such as lantern slides. 
The early glass positives were produced by the 
collodion process, and the deposit forming the 
image was white and the shadows clear glass, 
there being a backing of black velvet, cloth, or 
paint. 


GLASS, RUBY (See “Ruby Glass.”) 


GLASS, SILVERED 

Photographers and process workers are well 
advised not to prepare their own mirrors and 
prisms, but the question of silvering is im- 
portant. The silvered surface must be thick 
and durable to withstand the frequent polishing 
for removal of tarnish. Mirrors should be 
thoroughly warmed before polishing, and the 
polishing pad and rouge must be quite dry and 
warm. The very finest optical rouge should be 
used, and the pad should be rubbed on a clean 
glass plate before applying it to the mirror. 
The pad should be kept in a wide-mouthed glass 
jar with glass stopper when out of use, so that 
no gritty dust can reach it. The silvering on 
the hypoteneuse of prisms should be backed with 
an electro-deposit of copper and then varnished, 


GLASS, SOLUBLE (See “ Water-glass.”) 


GLASS, YELLOW (See “Yellow Glass,”’) 


GLASSWARE, PHOTOGRAPHING 
Photographically, glassware is similar to silver 
ware, and the instructions for lighting, etc., given 
under the latter heading apply almost as well 
to glass vessels. Glass may sometimes be 
improved by frosting or dewing, as described for 
silver ware, but in most cases it is advisable to 
fill the glass vessels with a non-actinic solution, 
in order to prevent the details and high lights 
on the far side conflicting with those nearest the 
camera. A non-actinic solution may consist of 
a very dilute solution of potassium perman- 
ganate, but it must be only slightly tinged, 
otherwise it will appear as ink. Another plan 


276 


Glossy Surfaces on Prints 


is to dust the glasses lightly with powdered talc, 
using this for partly filling up engraving in order 
to make it show more distinctly upon the nega- 
tive. The background should be of a dark tint. 

In process work, numerous expedients are 
resorted to for photographing glassware for 
catalogue illustrations. A piece of ice put 
inside the vessel will cause moisture to condense 
on the outside, and so stop reflections. Dabbing 
the glass over with putty is also effective on 
smooth surfaces, but does not avail with cut- 
glass. Coating the glass with a varnish and 
blackleading with a brush has also been resorted 
to. Spraying the glass with the aerograph also 
Setves the purpose. 


GLAZING PRINTS (See “ Glossy Surfaces on 
Prints;?”) 


GLAUBER’S SALT 

Another name for sodium sulphate (which see). 
First produced by Johann Rudolph Glauber, a 
German chemist, about 1661; hence the name. 


GLOBE LENS 

One of the earliest non-distorting, wide-angle 
lenses, introduced by Harrison, of New York, 
in 1862, and highly esteemed until superseded 
by the wide-angle rectilinear, Its chief defects 


were slowness (full aperture f/36) and liability 
to flare. It was symmetrical in construction, 
the outer surfaces of the two components being 
so placed as to form part of a sphere, as shown. 


GLOBE POLISH REDUCER (See ** Baskett’s. 
Reducer.’’) 


GLOSSY PAPERS 

These are almost always prepared with gela- 
tine. Their gloss may be enhanced in finishing 
by the procedure given under the heading 
“Glossy Surfaces on Prints.” A glossy surface 
possesses the advantage of imparting great depth 
and transparency to the shadows, and of render- 
ing all detail crisply throughout the scale of 
tones. It also gives greater visual contrast in 
the print. For this reason, prints with glossy 
surfaces are very desirable for reproduction pur- 
poses, and for many kinds of commercial photo- 
graphy, engineering subjects, architectural de- 
tails, etc. There are several papers on the market, 
both for daylight and for artificial light printing, 
with semi-glossy surfaces. 


GLOSSY SURFACES ON PRINTS 

For finishing prints with a glossy surface, a 
paper prepared with a naturally glossy surface 
should be employed. The most simple and 
satisfactory method of working is as follows: 
The prints, after fixing and washing, should be 
immersed in a formaline bath (formaline + oz., 
water 5 oz.) for two or three minutes, washed 


Glucose 


for a quarter of an hour, and then dried. A 
glass, celluloid, or ferrotype plate is washed and 
polished with a soft fabric, first rubbing on with 
a flannel a solution of 20 grs. of beeswax in I oz. 
of turpentine. The print is soaked in water 
until thoroughly limp, and then a liberal quantity 
of water is thrown on the polished plate, and 
the print placed face downwards on the plate, 
care being taken that there is plenty of water 
between the two surfaces. The print is next 
firmly squeegeed into contact, interposing a 
sheet of rubber cloth between the print and the 
roller squeegee. When quite dry, the print will 
leave the plate very easily, and its surface will 
possess a high gloss. This surface is hard and 
durable, due to the employment of the forma- 
line bath, but it is well to back the print with 
a waterproof sheet so as to prevent the mount- 
ant from affecting the glaze. 


GLUCOSE (Fr., Glucose ; Ger., Glycose) 

Synonym, dextrose, grape sugar. C,H,.0,. 
Molecular weight, 180. A thick, syrupy, yellowish 
liquid, obtained by the action of dilute sulphuric 
acid on starch. It was suggested as a developer 
or addition to developers for wet plates. 


GLUE, FISH (See “ Fish-glue.’’) 


GLYCERINE (Fr., Gilycérine ; Ger., Glyzerin) 

A colourless, odourless, thick liquid of charac- 
teristic sweet taste, miscible in all proportions 
with water and alcohol, and slightly soluble in 
ether. Glycerine as purchased from a chemist 
or at an oilshop is good enough for photographic 
purposes. It has many uses in photography, 
for example, in developing platinotypes, as a 
constituent of developers, as an addition to 
gelatino-chloride and collodio-chloride emulsions, 
in mountants, and to prevent films curling. 

In collotype work, glycerine is used for the 
* etching ’’ or damping of the plate previous to 
inking. A suitable solution consists of 3 parts 
glycerine to 2 parts water. 


GLYCEROL (See “ Glycerine.’’) 
GLYCINE, OR GLYCIN (Fr., Glycine ; Ger., 
Glycin) 


A developer, known also as paraoxyphenylgly- 
cin, having the formula C,H, OH NHCH, COOH. 
It appears in the form of glistening grey powder, 
which, when carelessly kept, turns to a brownish 
black and loses its developing powers. The 
powder is insoluble in plain water, but soluble 
in a solution of sodium sulphite, or on the 
addition of an alkali. It is a slow-working 
developer, having a factor of 7, and works after 
the manner of ferrous oxalate; it has the advan- 
tage of giving good clear negatives with little or 
no fog, and good density. It is widely used for 
stand and tank development and for the repro- 
duction of black-and-white subjects; it may be 
used in a one-solution or two-solution form. 


One-Solution Developer 


Hot water 30 OZ. 1,000 ecs 
Sodium sulphite 1},, 45g 
Potassium carbonate 24,, 90 ,, 


Glycin . . ° 3 ” 18 39 
The above is ready for use. 


277 


Goddard, John Frederic 


Another one-solution formula gives a stock 
solution in the form of a cream, and is known 
as— 

Hiubl’s Stock Glycine Solution 


Sodium sulphite 24 02. 688 g. 
dissolved in— 

Hot water ° <P ES 1,000 ccs. 
then add— 

Glycine. . banal i gee 275 g. 
Heat to boiling point, and add— 

Potassium carbonate . 5 oz. 1,375 2g. 


Add the potassium carbonate gradually in small 
quantities on account of the carbonic-acid gas. 
When cold, this forms a thin paste; when 
required for use, shake and dilute 1 part with 
12 parts of water, using more water for soft 
development and less water for hard develop- 
ment. For stand development, mix with 50 
to 55 parts of water. 


Two-Solution Developer 


A. Glycine 380 ers. 44 g. 
Potass. carbonate Thee ie IO Si3. 
Sodium sulphite 5 oz. 29Ge 
Water . : ZO) Wy ll 2000 oes. 

B. Potass. carbonate 245; 137 g. 
Water . . SAAD) Say | t.2 OU SeEe: 


For use, mix equal parts of A, B, and water. 
Potassium bromide is added in cases of over- 
exposure. 

Messrs. Newton and Bull have recommended 
glycine as a developer for all isochromatic plates, 
as follows :— 


Glycine : . sv  EQ2- Ets. 18g; 
Potass. carbonate . : 2 OZ. en 
Sod. sulphite (anhydrous) 240 grs. 22,, 
Potassium bromide rely MEO th, 
Water to 25 yw 1,000 ccs. 


Development is controlled by time, using a 
factor of 6. 

In process work, glycine is an excellent developer 
for collodion emulsion and for process dry plates, 
but it is expensive compared with hydroquinone, 
which is more generally used. 


GLYCOCINE (Fr., Glycocine ; Ger., Glykokoll) 

The decomposition product of the action of 
sulphuric acid on gelatine. It was used as a 
preservative for collodion dry plates. (See also 
“* Amido-acetic Acid.’’) 


GLYCOCOLL (See “ Amido-acetic Acid.’’) 


GLYPHOGRAPHY 

An electrotyping process invented by E. Palmer, 
of London, about 1844. Acopper plateis coated 
with a white composition consisting of white wax 
and zinc white, and the coating is scratcued 
through with needles so that the lines are formed 
in deep furrows. The plate is brushed with 
blacklead, and forms a mould for electrotyping. 
(See also ‘“*‘ Wax Process ’”’ and “‘ Cerography.’’) 


GODDARD, JOHN FREDERIC 
Inventor of the polariscope; improved the 
daguerreotype process by discovering (in 1840) 


Goetz’s Reducer 


the accelerating properties of bromine, by which, 
with iodine, he obtained a bromo-iodide of silver 
on the surface of the silvered plate, thereby 
reducing the necessary exposure to about one- 
sixtieth—from twenty minutes to twenty seconds. 
This invention, in conjunction with Fizeau’s 
gold chloride and ‘‘hypo” invigorator, made the 
daguerreotype a commercial success, as it then 
became possible to give reasonably short ex- 
posures, whereas previously long exposures were 
needed, and the sitter’s face had to be whitened 
with powder, and placed in full sunlight. 


GOETZ’S REDUCER 

A reducer for negatives introduced in 1894 
by H. Goetz. A strong solution is made by 
mixing 1 oz. of copper sulphate with 5 oz. of 
distilled water :— 


No. I— 
Common salt ‘ io PL OS, 28 g. 
Copper sulphate solution. 4 ,, Seas, 
Distilled water ‘ cD 44 DOLOOO Ces: 
No, 2— 
Sodium hyposulphite . 96 gts. 22 g. 
Distilled water 10°07" VE.000 Cos 


The carefully washed plate is placed for from 
twenty to thirty seconds in solution No. 1, then 
rinsed and transferred to No. 2, in which the 
reduction takes place, and the process should 
be well controlled, the action being a rather 
quick one. The longer the plate has been left 
in No. 1 the more rapid will be the reduction in 
No. 2. For slight over-exposure increase the 
salt and decrease the copper sulphate in No. 1; 
the contrary holds good in a case of under- 
exposure. Finally, the negative should be 
thoroughly washed. 


GOLD (Fr., Or ; Ger., Gold) 

Au. Molecular weight, 197. It occurs native 
in grains or nuggets. A heavy yellow or orange- 
yellow metal, which, as a metal, is not used in 
photography. Its salts are used for toning 
prints. Most of its salts are sensitive to light, 
particularly the chloride, in the presence of 
organic matter, and therefore all gold solutions 
Should be kept in the dark, 


GOLD CHLORIDE (Fr., Chlorure d’or; Ger., 
Goldchlorid) 

Synonyms, trichloride or perchloride of gold, 
auric chloride. AuCl,; HCl 4H,O. Molecular 
weight, 412. Solubilities: very soluble in water, 
alcohol, and ether. It occurs as needle-like 
yellow crystals obtained by dissolving metallic 
gold in aqua regia and evaporating the solution. 
The crystals are very hygroscopic, and should 
be kept in a stock solution. There is a brown 
form of gold chloride, AuCl, HCl *H,O, which 
contains less water than the yellow salt and is 
less hygroscopic. This should contain from 50 
to 51 per cent. of metallic gold. Both salts are 
used in toning. Gold chloride has a great 
tendency to form double salts with the alkaline 
chlorides, which are more stable. (See “Gold 
and Potassium Chloride’”’ and ‘“‘ Gold and Sodium 
Chloride.’’) 


GOLD AND ‘‘HYPO’’ BATH (See “ Gold 
Hyposulphite.’’) 


278 


Gold and Sodium Chloride 


GOLD HYPOSULPHITE (Fr., Hyposulfite d’or 
et de sodium, Sel de Gélis et Fordos ; 
Ger., Unterschwefligsdure Goldoxydulnatron, 
Goldsaiz) 

Synonyms, sel d’or, hyposulphite of gold and 
soda, AuS,0,Na,S,032H,0. Molecular weight, 
522. Solubilities, very soluble in water, almost 
insoluble in alcohol and ether. It occurs in white 
needles, and is obtained by adding a strong 
alcoholic solution of gold chloride to an excess 
of sodium hyposulphite. It was usually pre- 
pared in solution by adding a 2 per cent. solution 
of gold chloride to a 6 per cent. solution of 
“hypo.” It was used for toning or “ gilding ” 
the old daguerreotype image, and is sometimes 
recommended for printing-out papers. 


GOLD AND IRIDIUM BATH 

The addition of iridium and potassium chlorides 
to a gold bath has been recommended for toning 
prints, but as it presents no practical advantages, 
and merely increases the cost, it has found no 
general use, The following is used for toning 
ceramic substitution pictures, and gives a warm, 
black tone :— 


Iridium chloride - 34 grs. 3°95 g. 
Gold chloride pe BOA iets 
Lactic acid « 22) mia, 2: Coa, 
Distilled water to- . 20 oz L.O6OF >. 


GOLD AND PLATINUM BATH 

The addition of chloroplatinite of potassium 
to the gold sulphocyanide bath was stated to 
give rich black platinum tones, whereas, as a 
matter of fact, all that takes place is the more 
rapid deposition of the gold. A bath similar in 
composition to that given under the heading 
“Gold and Iridium Bath,” the iridium being 
replaced by potassium chloroplatinite, is also 
used in producing ceramic photographs. Plati- 
num baths are sometimes used after a gold 
toning bath for P.O.P. papers. 


GOLD AND POTASSIUM CHLORIDE (Fr., 


Chlorure dor et de potassium; Ger., 
Kaliumgoldchlorid) 
KCl AuCl, 2H,O or KAuCl, 2H,O. Mole- 


cular weight, 414. Solubilities, very soluble in 
water, alcohol, and ether. Vellowish needles 
obtained by mixing four parts of gold chloride 
in concentrated solution with 1-12 parts of 
potassium chloride, evaporating, and crystallising, 
It is used for toning. 


GOLD RESIDUES (See ‘* Residues.’’) 


GOLD AND SODIUM CHLORIDE (Fr., 
Chlorure @’or et de sodium ; Ger., Natrium 
goldchlorid) 

NaCl AuCl, 2H,O, or NaAuCl,2H,O. Mole- 
cular weight, 398. Solubilities, very soluble in 
water, alcohol, and ether. Yellowish orange 
crystals, obtained in the same way as the potas- 
sium salt (see ““Gold and Potassium Chloride”’), 
using 4 parts of gold chloride and 1 part 
of sodium chloride. Both these salts may be 
adulterated with free potassium or sodium 
chloride, which may be detected by dissolving 
them in absolute alcohol, when any alkaline 
chloride will be undissolved. 


Gold Toning 


GOLD TONING (Fr., Vivage a Vor; Ger., 
Tonen (Schénen) mit Goldsaiz) 

The purpose of the gold toning bath is to 
convert the somewhat unpleasant yellowish red 
colour of the fixed silver image into a more 
pleasing brown, purple or bluish purple. This 
has been erroneously described as “ gilding,’ 
whereas the action is purely chemical, the gold 
taking the place of the silver of the image, 
and the silver being converted into chloride in 
place of the gold. If instead of a plain solu- 
tion of gold chloride the auric chloride AuCl, 
were used, the reaction could be expressed as 
follows :— 


AuCl, + 3 Ag = 3 AgCl + Au 


From this it will be seen that one atom of 
gold replaces three atoms of silver, and the fine 
details in the high lights would disappear and 
the image lose considerably in vigour. If, on 
the other hand, the gold is reduced to the 
aurous chloride AuCl, the reaction would be 
represented by— 


AuCl + Ag = AgCl + Au 


and one atom of gold would replace one atom 
of silver. Ithas been stated that an intermediate 
aurous chloride, AuCl,, is formed, but it is such 
an unstable salt that its existence is doubtful. 
To convert any toning bath into the proper 
toning condition—that is, when the gold is 
reduced to the aurous state—it is “ripened” 
either by allowing it to stand or by the use of 
hot water to dissolve the salts, which should 
make the bath either neutral or distinctly 
alkaline. In the case of the sulphocyanide bath, 
a double salt of sulphocyanide of ammonium 
or potassium and gold is formed; this may 
also be in the auric or aurous state, and a 
similar chemical action takes place. Of recent 
years a more reasonable method of using the 
gold bath has been generally adopted, this 
allowing a definite quantity of gold to a definite 
area of print, instead of using one bath for a 
number of prints in succession and then adding 
fresh gold. It is important to wash prints well 
before toning, so as to free them from the excess 
of silver nitrate, which would decompose the 
gold chloride and prevent its deposition on the 
print. When a toning bath has been used, all 
the gold is not exhausted ; but some which has 
passed into a stable aurate will not deposit. 
Obviously this may be collected for the sake of 
the residues, or the old bath may be used 
instead of water to make a new bath, the former 
plan being preferable. (See also “ Residues.”’) 


GOLD TRICHLORIDE OR PERCHLORIDE 
(See *“‘ Gold Chloride.’’) 


GOLD AND URANIUM BATH 
A mixture which has been frequently sug- 

gested for obtaining warm black tones on matt 

surface print-out gelatine or collodion papers :— 
Gold chloride : 24ers. °25 g. 
Uranium nitrate ° ot eS wed Pie 
Sodium chloride i Toa Tan 
Sodium acetate ‘ nes Bap yee 
Distilled water to 1,000 ccs. 


Dissolve the gold and uranium in a little water, 


279 


Grain in Negatives 


neutralise with sodium bicarbonate, and add to 
a hot solution of the other salts. The bath is 
ready for use when colourless and cold. 


GOUPIL PROCESS 

A method of making facsimiles of water- 
colour drawings. A photogravure plate is care- 
fully inked by hand with small dabbers or tam- 
pons, and in the more delicate parts with 
brushes, using differently coloured inks accord- 
ing to the character of the portions of the plate 
to be inked. When the inking is complete the 
coloured print is obtained at one impression. 
The plate is then cleaned and inked again for 
the next picture. This method of printing is 
very slow and costly, as skilled artists have to 
be employed for colouring the plates. The 
results, however, are very fine, and in some 
cases hardly distinguishable from the original 
water-colour drawing. The process is still 
practised. 


GOUPIL GRAVURE 

A photogravure process suggested to Goupil 
and Co., of Paris, by W. B. Woodbury, about 
1870, and largely worked afterwards by that 
firm. <A gelatine relief was made in the same 
manner as for the Woodburytype process, 
except that a fine gritty powder was added to 
the gelatine to give the necessary grain. From 
this relief a mould was taken and an electrotype 
shell deposited on it. 


GRADATION 

That variation of tones in a print by which 
are suggested differences in colour and in light 
and shade. A print has a long scale of gradation 
when there are many intermediate tones between 
deepest shadow and highest light. (See ‘* Key.’’) 


GRAIN IN COPYING 

Copies of photographs frequently have a 
‘grainy’ effect, due to the dry plate reproducing 
the grain of the paper on which the original 
photograph was printed. To reduce the effect as 
much as possible, the original should be placed 
for copying in a good diffused front light; it is 
the character of the lighting that is generally 
to blame when the grain is reproduced promi- 
nently, as the stronger the light from one point, 
usually one side, the more pronounced is the 
grain. A method of obviating grain is to smear 
the face of the original with glycerine and 
squeegee it face downwards on plain glass, the 
copy being then made through the glass. 

In process work, the suppression of grain is 
more easily attained, now that the use of the 
electric arc has become common, than it was 
when daylight copying was in vogue. By the 
use of two arc lamps, one on each side of the 
copy, the illumination can generally be adjusted 
to overcome the effect of the grain. Also the 
originals may be photographed under plate glass. 


GRAIN IN NEGATIVES 

In the early days of rapid plates a grain was 
perceptible in the negative, it being coarser as 
the speed of the plate increased ; but the defect 
has now almost vanished, although it may still 
be produced under certain conditions. “ Grainy ” 
negatives are more frequent in hot weather than 


Grained Negative 


in cold; in the summer, and particularly when 
development is forced and the plate happens to 
be under-exposed, excessive coarseness of grain 
may often be seen. The temperature of the 
atmosphere during the drying of the negative 
affects the grain, and the more quickly a nega- 
tive is dried the coarser will be the grain; there- 
fore, when a negative is to be used for printing 
upon glossy paper, or lantern slides are to be 
made from it, the cooler the atmosphere employed 
for drying the better. One theory (there are 
several) is that when negatives dry slowly on a 
hot day, the gelatine becomes partly decom- 
posed, allowing the particles of the silver bromide 
to come together; these particles have an 
affinity for each other, and are enabled to come 
together when the gelatine which keeps them 
apart has been to some extent destroyed. Thus 
the particles form coarse particles, and impart 
to the negative a “‘ grainy ” or woolly appearance. 
Excess of alkali also increases grain ; therefore, 
in order to produce a negative as grainless as 
possible, let the exposure be full, use a normal 
developer at no _ higher temperature than 
65° F. (18° C.), and dry as quickly as possible 
in a cool, clean current of air, 

In process work, it is a disadvantage to use a 
plate that gives too granular an image. Hence, 
process dry plates are relatively slow in order 
to secure a fine-grained emulsion. In collodion 
emulsion work also, the grain must be kept fine. 


GRAINED NEGATIVE 


A term often employed to denote a half-tone 
process negative, or a negative made through a 
ruled screen for breaking up the image into a 
fine grain, 


GRAINS PER OUNCE 

See under the heading “ Solutions, Making 
up,” where the number of grains per ounce of 
solutions of the usual “ percentages” will be 
found. 


GRAM, OR GRAMME 

A metric weight, equivalent to 15-432 grains 
avoirdupois, apothecaries’, or troy; written g. 
or gm. in formule. (See also “Weights and 
Measures.’’) 


GRANULATION, OR GRANULARITY (Fr., 
Granulation ; Gr. Granulieren) 

A term usually applied to an image of which 
the grain is coarse and distinctly visible to the 
naked eye. It may be due to the emulsion or 
to the action of the developer. It is also occa- 
sionally used for images broken up into a 
gtain photo-mechanically, 


GRANULOTYPE 

A term applied to a half-tone etching on 
grained zinc, the image being formed by means 
of the bitumen process, printed under a tone 
negative. 


GRAPHOSCOPE 

An instrument containing a double convex 
lens large enough to permit both eyes at the 
same time to look through it at a single photo- 
gtaph, in this way obtaining, it is said, an 
illusion of relief, but not that solidity observable 


280 


Green Glass 


in a stereoscope. The suggestion of relief may 
be due to the non-achromatic lens causing over- 
lapping of the different rays. 


GRAPHOTYPE 


A process suggested by A. H. Wall, in which 
a block of compressed chalk was drawn on with 
a specially prepared ink, which hardened the 
chalk wherever the lines were made, whilst the 
clear parts could be brushed away until a high 
relief printing block was obtained. ‘The chalk 
no doubt contained size, and the ink some hard- 
ening substance, such as chrome alum, tannin, or 
formaline. In another process of this kind the 
block of chalk is treated with water-glass, to 
harden it after brushing it into relief, 


GRATING, DIFFRACTION 
tion Grating.’”’) 


GRATING, PRISM 


A diffraction grating on the hypotenuse of 
a prism of 60°, used for direct-vision diffraction 
spectroscopes. An ingenious method of making 
these gratings was devised by Thomas Thorp, 
of Manchester. He flows a plane metallic 
diffraction grating with celluloid, which when 
dry is stripped off as a film and cemented to the 
prism ; it gives an image hardly inferior to that 
produced by the original grating. 


GRATING, SCREEN 


A term sometimes applied to the ruled screen 
used for half-tone process work. 


GREEN FOG 


GREEN GLASS 


Printing through green glass increases the 
contrasts on P.O.P. ‘The use of coloured glasses 
was suggested by Lemann in 1861, since when 
it has been repeatedly adopted for obtaining 
rich prints from thin and flat negatives. About 
1890 the use of greenish yellow glass was advo- 
cated for obtaining, in conjunction with matt 
papers and the uranium toning bath, not only 
vigorous prints, but also black tones resembling 
platinotype. Glossy P.O.P. also prints very 
much brighter and better under green glass, 
and the method is of great advantage when 
valuable negatives of a flat, thin, or ghostly 
character are used and intensification is not 
allowable. A green glass cuts out the violet and 
deep blue rays of light, allowing the bright blue, 
green, and yellow rays to travel through the 
negative and act upon the sensitive paper, with 
the result that the organic salts of silver are 
acted upon more than the chloride. ‘The organic 
salts have a shorter scale of gradation than the 
chloride has, hence the prints” have stronger 
contrasts and the shadows are rither than would 
otherwise be the case. The most suitable shade 
of glass for the purpose is that known as “ signal 
gteen”’ or “single flashed chromium green.” 
With the green glass, which is placed over the 
negative, printing is considerably prolonged. 
The method answers only with print-out silver 
papers. Green glass has also been advocated in 
place of ordinary glass for dry plate making ; 
it has several advantages, one being that it 
prevents halation, 


(See ‘‘ Diffrac- 


(See “ Fog, Colour, etc.’’) 


Green Tones 


GREEN TONES 


Green tones are generally difficult to obtain 
and not of great permanency except by the 
carbon process. Carbon tissue in many shades 
of green may be purchased, and greens by the 
ptocess are easy to obtain, of even quality and 
quite permanent. 

P.O.P.—The green tones obtainable on P.O.P. 
are uncertain as to exact tone, and they are not 
permanent. The best method is to tone as 
black as possible in the usual way, and then to 
stain the print with an aniline dye. Another 
method is to print very faintly, and then, without 
washing, immerse the print in a 10 per cent. 
solution of potassium bromide for three minutes. 
The faint image is then developed with a metol- 
hydroquinone developer as used for bromide 
paper, then washed and fixed in the usual way, 
without toning. 

Bromide Paper.—The following is a typical 
method, which not only gives a good green, but 
intensifies considerably at the same time. Make 
Io per cent. solutions (48 grs. in 1 oz. of water) 
of (1) uranium nitrate, (2) ammonio-citrate of 
iron, (3) potassium ferricyanide, (4) nitric acid. 
For use mix together No. 1 12 drops, No. 2 
12 drops, No. 3 24 drops, No. 4 24 drops, and 
add water to make 1 oz. Immerse print until 
of the desired colour, wash, and dry. A much 
brighter green may be obtained by mixing 
together 4 oz. of No. 2, $ oz. of No. 3, and 5 oz. 
of a 10 per cent. solution of acetic acid. Tone, 
rinse, and transfer to a Io per cent. solution of 
chromic acid; rinse, and immerse in a 5 per 
cent. solution of alum; then wash and dry. 


GREENHOUSE AS STUDIO (See ‘“ Studio 
Design and Construction.’’) 


GREENLAW’S PROCESS 

A modification of the calotype process for 
obtaining paper negatives. Thin paper was im- 
mersed for about an hour in a solution of potas- 
sium iodide and potassium bromide, containing 
sufficient iodine to give it a dark claret colour. 
It was then dried, sensitised as required in an 
acidified silver nitrate bath, rinsed, and again 
dried. After exposure in the camera, the paper 
was developed with gallo-nitrate of silver, rinsed 
well, fixed with “hypo,” and washed. 


GROUND GLASS 

Besides its use for the focusing screen (which 
see), it is also employed to diffuse the light in 
dark-room lamps, in enlarging apparatus, and 
in printing. Sometimes itis employed in glazing 
the studio, when direct sunshine has to be 
excluded or an objectionable view blocked out. 
A piece of ground glass may be placed behind 
the negative in the retouching desk, to give a 
softer and more uniform light. Ground glass is 
also used to give a matt surface to P.O.P. prints. 


GROUND GLASS, COPYING THROUGH 

In making half-tone process blocks from a 
half-tone print, very finely ground glass may be 
used to prevent the crossing of the two dot 
images from forming an objectionable pattern. 
The plain side of the glass is placed in contact with 
the print, and the ground side is rubbed with a 
trace of glycerine. 


281 


Group Arrangement 


GROUND GLASS PLATES (Fr., Plaques @ 
verre dépolt; Ger., Mattglasplatten) 

Plates having the emulsion coated on finely- 
ground glass instead of plain glass, or on a 
specially prepared matt substratum. The latter 
idea was originated by E. J. Wall. Softer prints 
are obtained from the resulting negatives, while 
the matt surface offers great facilities for work- 
ing on with pencil. Such plates are especially 
suitable for stereoscopic and other transparencies. 
Plates coated with a matt emulsion beneath the 
sensitive emulsion are obtainable commercially 
under the name of ‘‘ Matt-ground,” or “‘ M.G.” 

In process work, thick plate glass ground on 
one side with emery powder is used as the sup- 
port for the collotype printing film. 


GROUP ARRANGEMENT 

There is some truth underlying the saying 
that “two are a group, three a crowd.” The 
difficulty of securing a perfect rendering of a 
single figure is enormously added to by every 
further addition. In fact, when many figures 
are to be included at the same time it is hardly 
possible to secure anything more than a num- 
ber of mere portraits. When the group is a 
small one it is often possible to secure a natural 
atrangement in which each member has some 
common point of interest or occupation. In 
such a case, however elaborately the sitters may 
be “ arranged,’’ the result should appear natural 
and fortuitous, as though it had merely been 
taken at a happy moment. The figures must 
not be placed with any appearance of balance 
or symmetry having been deliberately aimed at, 
but at the same time they must not seem in- 
dependent and isolated. 

In the case of larger numbers, such a homo- 
geneous composition is practically out of the 
question. The worst arrangement that can be 
made is, unfortunately, the most common one. 
This is placing the figures in one or more straight 
lines right across the picture. A narrow band 
of small figures with a wide expanse above and 
below is never satisfactory. It is better, when- 
ever possible, to take advantage of a sloping 
bank or a flight of steps, so as to increase the 
height of the group on the plate. Such a group 
must not appear ill-balanced or lop-sided. 
Another common fault to be avoided is the use 
of a short-focus lens, which exaggerates the 
difference in apparent size between the nearer 
and more distant figures. A long-focus lens 
and a more distant standpoint give a more 
natural effect. 

A football or cricket team, a wedding group, 
a family party, and so on, admit only of a more 
or less formal treatment, the desideratum being 
a collection of good portraits. This does not 
apply to renderings of groups for what may be 
called pictorial purposes, such as fishermen on 
the beach or women in a market place. In 
such cases any attempt at deliberate arrange- 
ment is often impossible, and oftener inadvis- 
able. ‘The only satisfactory method is to watch 
carefully the ever-varying arrangement of the 
figures composing the group and to seize the 
most promising opportunities that offer. Appro- 
priate and characteristic poses should be watched 
for, with careful regard all the time to the relative 
positions of the members of the group. The 


Grun Lens 


figures will from time to time naturally fall into 
satisfactory arrangements, and these moments 
must be waited for and taken instant advantage 
of. As has been said, the difficulty of obtaining 
a perfect arrangement increases with the number 
of figures included, but it is seldom possible to 
make this arrangement deliberately without 
introducing a suggestion of unnatural posing 
and stiffness. In a satisfactory group arrange- 
ment it must be remembered that all the figures 
must not claim equal attention; some should 
be prominent and others duly subordinate. 


GRUN LENS 

A fluid lens (which see), said to be filled with 
cedar oil; it works at a large aperture and 
has been used for theatrical photography. 


GUAIACOL (Fr., Gaiacol; Ger., Guajakol) 

Synonym, methylcatechol. A faintly yellowish, 
limpid liquid obtained from beechwood creosote 
by fractional distillation. It was supposed to 
be a developer, but more careful purification 
proved that it was an impurity that acted, and 
not the guaiacol itself, 


GUAIACUM RESIN 

The resin obtained from guaiacum or lignum 
vite is sensitive to light, and North has patented 
a process in which guaretinic acid, obtained from 
the above, was the light-sensitive compound with 
or without the admixture of dyes. It has found 
no practical application. 


GUM CUTCH (See ‘‘Catechu.’’) 
GUM ELASTIC (See “ Indiarubber.’’) 


GUM GALLIC PROCESS 

A dry collodion process used by Hardwick in 
1860, and improved by Manners Gordon in 
1868. The plate is edged with albumen and 
coated with collodion, to each ounce of which is 
added 1 gr. of cadmium bromide; next it is 
sensitised in a silver bath in the usual way. 
After that the following gum gallic solution is 
used as a preservative :— 


A. Gum arabic 20 gts. 173 2 
Sugar candy . Mae et gy oe 
Water : 6 drms. 21 ccs. 

B. Gallic acid 3 ers. ae, 
Water 2 drms. 7 ccs. 


A and B are mixed together and poured over 
the plate, this being next drained and allowed 
to take its own time to dry. The exposure 
necessary is from four to twenty times that for 
a wet plate. The developer specially recom- 
mended is :— 


A. Gelatine . 64 grs. 4 g. 
Glacial acetic acid 2 OZ. 57 ccs. 
Water. ; AeA fg 400 ,, 

B. Iron protosulphate . 30 ers. 2°e, 
Water : : 1 Oz; 28 ccs. 


One part of A is mixed with three parts of B, 
preferably one or two days before use. Before 
developing, immerse the plate in lukewarm water 
for a short time in order to soften the gum. 
Additional density is generally desirable and is 
obtained with a pyro-silver intensifier. The 
plate is finally fixed in “ hypo,” and washed. 


282 


Gums and Resins 


GUM OZOTYPE 
Gum.’’) 


GUM PLASTIC (See “ Guttapercha.”) 


GUM SILVER PROCESS 

A “plain paper” printing process by means 
of which print-out pictures may be obtained on 
almost any kind of paper, ordinary writing-paper 
answering quite well. Three solutions are 
required for sensitising :— 


(See “‘Ozotype Process, 


No. 1. Powdered gum arabic 120z. 54g. 
Water . ; > 98" Seo ome: 

No. 2. Solution No. 1 . 84° Tins oor 
Glacial acetic acid . 50 __,, Magee 

No. 3. Silver nitrate . » 15. Bra eras 


Water, distilled 


In preparing solutions Nos. 1 and 3, the gum 
and the silver must be pulverised. Add No. 3 
to No. 2, mix well together, and apply it with 
a fairly stiff brush to the paper, which is then 
dried in the dark; a brush bound in metal 
should not be used, but if none other is avail- 
able see that the metal binding does not touch 
the solution or the paper. The paper prints 
well as soon as dry, but better still, and the tones 
are richer, if used about thirty hours after pre- 
parting. The paper is printed in the same way 
as ordinary P.O.P., and good red tones may be 
obtained by printing to a suitable depth and 
fixing in a weak “hypo” solution (48 grs. in 
5 oz. of water). Colder and purplish tones may 
be obtained by toning in a gold or platinum 
bath, or even in a combined bath. ‘The finished 
tone depends largely upon the quality of the 
negative. 


GUMS AND RESINS 

The photographer uses gums and resins chiefly 
in the form of varnishes. 

Amber, a fossil resin, ranging in colour from 
colourless to reddish-brown, is slightly soluble 
in ether and turpentine; treated in the same 
way as copal in varnish making, it dissolves in 
turpentine, petroleum and benzine. 

Anime, or Zanzibar copal, is of two kinds, 
fossil and “recent,” the former being superior ; 
of pale yellow or yellowish-brown colour and 
having a rough surface-called ‘‘ goose skin.” It 
is very hard, and, for varnish making, needs to 
be treated in the same way as copal; but it is 
slightly soluble in ether, benzine, chloroform, 
cold turpentine, etc. 

Copal, a fossil gum, of pale yellow colour, hard 
and transparent; soluble slightly in cold tur- 
pentine and fully soluble in turpentine when fused 
or “run” in a copper pan over a fire, a process 
that must be left to the varnish manufacturer. 

Dammar is known in several forms, ranging 
in colour from colourless or pale yellow to dark 
brown and black. It is soluble in oil, ether and 
benzene, . 

Dragon’s blood is of various kinds, the chief 
being of blackish-brown colour and being in 
sticks about 1 in. thick; soluble in alcohol, 
benzene, chloroform, carbon bisulphide, etc. 

Elemi is of many kinds and of a white or 
greyish appearance; it is soluble in alcohol. 

Guaiacum is described under its own heading. 

Gum arabic, small rounded nodules of yellow 


. 50 mins. 3 ccs. 


Gum-bichromate Process 


or brownish-yellow colour, is soluble in water 
but insoluble in alcohol. 

Gum benzoin, or gum benjamin, occurring in 
large blocks of grey or brown colour, with almond- 
shaped particles of a cream colour, is easily pul- 
verised between the fingers, and has a fragrant 
odour; soluble in alcohol and slightly so in 
ether and turpentine. 

Gum sandarach, a soft, bright gum, resembles 
tears or pears in shape, and is semi-transparent ; 
soluble in alcohol, and slightly so in benzine, 
petroleum, and turpentine. 

Gum tragacanth, or gum dragon, moss-like 
pieces of whitish colour, is opaque, hard, and 
tough; it forms a thick emulsion with water. 

Lac is a brown gum, known in many forms— 
including shellac (shell lac), seed lac, lump lac, 
stick lac, etc.—which are prepared from a 
resinous incrustation on the twigs of certain 
trees. It is soluble in alcohol and ether, and 

artially soin turpentine. White lac or bleached 
ac is used in preparing colourless varnish. 

Mastic is in the form of tears of a pale yellow 
colour, brittle, and easily melted; soluble in 
alcohol and turpentine. It is used in preparing 
mastic varnish. 

Resin, an amber-coloured or brown oxidation 
product of turpentine, is brittle, easily melted, 
of lustrous appearance in a thin coat, and is 
soluble in alcohol, turpentine, etc. 


GUM-BICHROMATE PROCESS 

Familiarly known as “‘ bi-gum,”’ this process 
depends on principles first laid down by Poitevin 
in 1855. Briefly, it consists in coating paper 
with a mixture of gum and pigment sensitised 
with potassium bichromate solution. This 
paper is printed under a negative, the bichrom- 
ated colloid becoming more or less insoluble in 
proportion to the light action. In this way a 
print may be obtained with a single coating, but 
it is usual to re-coat the print thus made and 
again print and develop. This may be repeated 
almost indefinitely, either for the purpose of 
reinforcing certain parts of the image, or for 
producing prints in more than one colour. The 
paper used must be well sized, in order that the 
pigment may lie on the surface and not sink into 
the substance of the paper so as to stain and 
degrade the high lights. If the paper is not 
already sufficiently sized a formula suggested by 
Mummery is 3 to 5 percent. of gelatine in 
water with 5 drops of formaline to the ounce. 
This is brushed evenly over the paper. 

The experienced gum worker frequently 
evolves his own formula for coating the paper. 
It is best to arrive at this experimentally by 
proceeding in some such manner as the follow- 
ing: 2 oz. of good clean gum arabic in tears is 
enclosed in a muslin bag and suspended in 6 oz, 
of cold water for about two days. This provides 
the gum solution. Next, a saturated solution of 
ammonium or potassium bichromate is made. 
Lastly, the pigment may take the convenient 
form of moist water colours in tubes. A mix- 
ture may then be made of 10 parts gum solution, 
5 parts bichromate solution, and a quantity 
of the pigment to be judged always by the length 
of the “‘worm’” of colour squeezed from the 
tube. Less bichromate will make the paper 
less sensitive. The ingredients of the mixture 


283 


Gun and Revolver Cameras 


must be thoroughly incorporated by rubbing 
down on a slab or sheet of glass with a palette- 
knife. 

The sized paper is coated with this mixture 
by means of a camel-hair mop, a hog-hair softener 
being passed over the surface afterwards in both 
directions to make it smooth and even. All this 
must be done quickly before the coating hardens. 
After about half an hour the paper should be 
thoroughly dried by heat and placed in a calcium 
tube if it is to be kept, although it is best to use 
it as fresh as possible. It must be borne in 
mind that the paper is very sensitive to light. 

Duration of printing depends to some extent 
on the composition of the coating. As the image 
is not visible an actinometer must be used as in 
carbon printing, or a piece of P.O.P. exposed 
simultaneously under a negative similar in print- 
ing speed to the one in use. As a rule, the 
bichromate paper will be sufficiently exposed 
when the P.O.P. image looks of the right density. 

The gum print is now placed face downwards 
in a dish of cold water. The pigmented gum 
will soon begin to leave the paper slowly. It is 
here that the worker begins to exercise that 
control over the development that constitutes 
the chief value of the process. He may employ 
cold or tepid water by laving, spraying, spong- 
ing, or brushing. By such means he retains only 
such of the pigmented gum as he requires for the 
rendering of his idea of the subject. 

If further printing is contemplated the print 
is dried and the processes of coating, printing, 
and developing repeated as before. Here comes 
in the difficulty of obtaining perfect registration 
of the second or subsequent images, and some 
device is necessary for securing that the print 
shall be replaced exactly in its original position 
on the negative. Even then there is the expan- 
sion and contraction of the paper to be reckoned 
with. 

When the final development is complete the 
print is soaked in a 5 per cent. solution of potash 
alum to remove the bichromate stain, and then 
rinsed in water. 

The use of various papers, the number of pig- 
ments available, the different effects resulting 
from modifications in coating and development, 
the power of multiple printings in one or more 
colours—all these afford opportunity for con- 
siderable exercise of control over the final result. 
But the very existence of these variable elements 
precludes the possibility, even if it were desir- 
able, of laying down any hard and fast rules for 
working the process. The individual worker 
must gradually formulate his methods by careful 
experiment and observation, in which case he 
will ultimately find the process most plastic, 
interesting, and valuable. (See also ‘‘ Arabin 
Gum-bichromate Process.’’) 


GUN AND REVOLVER CAMERAS (Fr., 
Fusil photographique, Révolver photo- 
graphique, Chambre révolver ; Ger., Feuer- 
gewehr-kamera, Revolver-kamera) 

The photographic revolver—the first instance 
of an efficient automatic apparatus for chrono- 
photography—was designed in 1874 by P. J. C. 
Janssen, the astronomer, to obtain a record of 
the transit of Venus. The observation was 
made in Japan, the instrument being placed 


Gun and Revolver Cameras 


under cover, as shown at A, and directed on a 
heliogtat, to keep the sun’s image stationary. 
Forty-cigut pictures were taken in succession 
on a circular plate, which was caused to make 
one revolution in seventy-two seconds, and 
etopped at the correct intervals by a Maltese 


A. The Janssen Photographic Revolver 


cross movement. The exposures were given by 
a rotating disc with twelve openings, moving 
at a different speed to the plate. A fixed 
partition, having a single aperture, was placed 
between the plate and the shutter disc, so that 
a different portion of the plate, then at rest, 
was exposed each time an opening in the shutter 
passed the fixed aperture. The operation was 
repeated four times to obtain a satisfactory 
record, On this model Marey founded later his 
photographic gun B. A long-focus lens was 
placed at the end of the barrel, thus rendering 
it feasible to photograph small objects from a 
distance, and the tube was arranged to telescope 
for focusing. The clockwork mechanism is 
illustrated at C, the back cover being removed. 
On pressing the trigger EH, a circular shutter 
with one aperture commenced revolving. Be- 


B. Marey’s Photographic Gun 


hind this rotated a disc F with twelve openings 
(only half is here shown), the sensitive plate 
revolving at the back of the disc by friction. 
The perforated disc and plate were moved 
intermittently by a pawl G, on an arm worked 
by an eccentric, and each time one of the openings 
in the disc F came to rest in line with the lens 
the aperture in the shutter passed in front of 
it, making an exposure. During its movement 


234 


Guttapercha 


the plate was protected from light by the opaque 
part of the shutter. (See also “‘ Chrono-photo- 
graphy.”’) 

Detective cameras and naturalists’ cameras 
of various kinds have been proposed from time 
to time under one or other of the names given 
at the head of this article. 


GUN-COTTON 

A nitro-cellulose, the hexanitrate, which is 
extremely explosive. The term is sometimes 
wrongly applied to pyroxyline. 


GUTTAPERCHA (Fr. and Ger., Guttapercha) 
A natural product having many similarities to 
indiarubber, but capable of being made plastic 
and malleable by heat, and retaining, when cold, 
any shape given it while hot. Whereas gutta- 
percha is plastic, indiarubber is elastic; and 
whereas indiarubber easily combines with sul- 
phur, guttapercha will neither combine nor 
intimately mix with that substance. Gutta- 
percha is the coagulated juice of the Isonandra 


C. Mechanism of Marey’s Gun 


gutta, which grows in the tropics, particularly in 
the Malay district. Its principal uses in photo- 
graphy are as a material for dishes and bottles 
to contain hydrofluoric acid, and as a mountant, 
For the latter purpose, a piece of very thin sheet 
guttapercha, the size of the print, is placed on 
the mount, next the print is laid over it, and 
then comes a sheet of blotting-paper, over which 
a hot iron is passed slowly and firmly. The heat 
softens the guttapercha, which then adheres to 
both mount and print. An objection to the 
method is the liability of the guttapercha to 
perish. 

A cement, made by dissolving 2 parts of 
shredded guttapercha and 2 parts of powdered 
Syrian asphalt in a mixture of 10 parts of oil 
of turpentine and 5 parts of carbon bisulphide, 
makes an excellent cement for leather and other 
materials. . 

Guttapercha has been used for coating paper 
in order to transfer collodion films. It has also 
been used for stripping negatives, instead of 
using rubber solution. By the addition of gutta- 
percha to collodion the latter is rendered not 
only tougher, but more sensitive. 


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